have to reboot as screen goes black and system freezes

After doing one the usual "updates", system log out fine, but start up was another story, system freezes on start up and screen goes blank and then black' nothing happens, you hear the system is on, but you can't log in or do anything else, until i have to take the power cable off without battery and re-start again, then the vaio sign comes on, a minute later the screen comes with the Unbutu GNU GRUB VERSION 1.99 12 UNBUTU 5.1 THEN IT SAYS UNBUTU, WITH LINUX 3.0.0.32 GENERIC, AND ETC, CHOOSE ONE AND THEN IT STARTS AFTER ALMOST 10 MINUTE ORDEAL. i HAVE TRIED EVERYTHING, HAVE TAKEN HOURS READING INFO REGARDING THIS ISSUE, A LOT OF PEOPLE POSTING SOLUTIONS AND YET NOTHING HAPPENS, MY SYSTEM WORKS FINE, JUST TWO TIMES, MY SYSTEM SHUT DOWN FOR NO APARENT REASON. i NEED HELP, NEW TO LINUX AND MY FRIEND WHO INSTALLED IT PASSED AWAY; i NEED TO FIX THIS MYSELF. HEEEEEEELP!!!!