Ubuntu 10.04 Reboot Loop

Did you MD5 test the ISO you downloaded?
Did you check the CD for defects?
Have you tested your RAM?

As stated above most of the times booting problems are caused by hardware problems.

As there are other possibilities, as well...
...What type of medium have you installed Ubuntu to? An internal or an external hard disk? And did you install it on a separate partition of your hard disk?
Some BIOSses seem never to have been tested using USB disks from their vendor.

On very old computers the BIOS wasn't able to load the full boot loader when it was too far from the beginning of a really big hard disk. But I think this should only affect really old computers.

Any information might help to track down the problem.

Another information that might be important: Is the command line completely empty or does it begin with a prompt like

~#

or

grub:

To actionparsnip: I both MD5 tested the ISO and checked the CD for defects. I only know how to test RAM with an operating system, so I don't know how I can test it without Ubuntu or Windows running.

To PeterPall: I tried to install Ubuntu to an internal Hard disk connected by a sata cable. All the parts are brand new, so as you said, I don't think it would be a problem with an outdated BIOS, but I'm not sure. And the command line is is just completely blank.

Thank you to both of you so much for your help and concern. I'm sorry if there's anything else important I left out, and if you need anymore information, I'd be obliged to provide it. The only other thing that comes to mind that I might have left out for now is that the first time I tried to install the 64-bit version of Ubuntu, rather then go into a reboot loop, it would freeze at the "Loading Operating System..." screen, but after I reinstalled, it goes into a reboot loop. Also, when I first tried to install Ubuntu, it had some problem recognizing the Hard drive, but I fixed that by plugging it in a different Sata port.

I had the same problem. It could just be a bad install. Just reinstall and see if it works.

What I can tell you is how booting a PC works in general. It is always good to know as much about a problem as you can.

The only thing the BIOS, the program that is built into your computer, does do after initializing the hardware is loading the first 512 Bytes (these bytes are often named MBR) from the first hard disk it can find - and hoping that it might find a program there it tries to execute this code.

512 bytes is not enough to contain much - and besides that half of these 512 bytes is used for the partition table that tells how the hard disk is split into partitions. So these 512 bytes contain a program that loads the next few bytes of a program that loads the boot loader that in turn is intelligent enough to load the actual operating system.

The boot loader that can load linux, windows and allows you to choose which of them to load is named GRUB, the Grand Unified Boot Loader.

Your problem seems to occour very early in this process: The BIOS tells that it will load the operating system, but Grub has not been able to tell you that it is starting up lest did display a menu which allows you to choose which operating system to boot.

One problem that may extremely rarely occour is that - I think it was DOS 3.0 - introduced a flag in the partition table that tells you which partition is bootable, and which is not. And if this flag can be set when partitioning the hard disk you should try it: Originally it was there to tell the bios which partitions not to try when loading the operating system. But it was almost never used by BIOSses, even in the earlier days.

---

For the memory test: I think on the first menu that is displayed when booting from the UBUNTU installer CD there should be an entry that starts memtest86, a memory tester that resides in the graphics memory --- and that will automaticaly test the whole rest of your computer's memory as through as it can - until you are confident enough your RAM is working and abort the test.

---

What you can try is to
 - Install Ubuntu from the alternate install CD: The alternate install CD slightly differs in some points and might work around a bug in your Hardware
 - make sure no unnecessary removable media is plugged in into your computer during install and the first try to boot it up, just to be completely sure that the boot loader won't try to install itselves there instead of on the hard disk
 - Look into the BIOS if it is set up to try to boot from the hard disk Ubuntu is installed to
 - Use the newest beta of Ubuntu 10.10: Very first in the process of creating a new Ubuntu traditionally one update fails - if you try to attempt this update until somebody finds out and fixes this problem. But as this event already has occoured about two months ago and since them 10.10 has proven to be rock-stable to me --- why don't give it a try?

Just because it works for you doesn't mean it will work for all.

Think of Linux as driving a car. Your "works for me" scenario is driving over the speed limit. Inexperienced drivers are newbies, and channel ops, forum mods and experienced users are the road/traffic authorities.

Speeding might get you somewhere faster, but it is dangerous to do so. Sometimes speeding is not really faster, as you still have to stop at lights and others going the speed limit actually catch up to you.

You may speed occasionally and not crash, however many, many people each year do crash while speeding.

Speeding is also far more dangerous if you are an inexperienced driver who does not know how to handle problems if they arise.

The road/traffic authorities have speed limits and these speed limits are advice based on their research and knowledge of the risks.

So you see, while your solution may work for you, it is not necessarily a good idea. Suggesting your solution to an inexperienced user increases the risk of something going terribly wrong, and that user has not got the experience to correct the problem.

We who are warning you against advising your solution are doing so for a good reason. We've seen the problems that "Works for me" solutions cause. We are the ones that are usually left to try clean up the mess.

Please, stop creating the mess, and we will all be happier.

For the other question: Installing windows after installing Ubuntu will overwrite Ubuntu's boot loader with the windows one - so you might have to use some trickery to make GRUB --- and therefore Ubuntu --- boot again: https://help.ubuntu.com/community/GrubHowto
 Installing windows first and then installing Ubuntu should be the easier way: Grub will automatically detect your windows installation and will ask you which operating system to boot.

Generally installing both operating systems on two partitions on the same system is a good Idea - and many of my collegues are doing this.