Webuser Forums: Please help! Computer won't restart/shutdown, font change .txt firefox, weird behaviors etc

About my computer: custom build computer build by professionals on ncix dot com, windows XP Home Edition service pack 2 . AMD 2.1 mhz processor, 1 GB RAN, 320 GB seagate HD (it has 58% space available), File fragmented only 1%, 1.96 virtual memory available. 8-9 months old

It all started when i updated windows update on april 14 and also installed youtube uploader and the the problem started right after 2 days ago later then that. I uninstalled youtube uploaded but the problem still persist. what happens is the computer works fine for the whole day but after 9-10 hours or more for some reason it does all kinds of weird things. For example like first, on a saved notepad .txt the place where the name of the .txt is disappears (where the name and Red X mark is to close whatever your using). Even if i close and re-open it, its their and it happens basically to all programs, files I open and including firefox browser. Then it gets even worst like when i re-open a saved .txt file the font changes and also the font changes on firefox also automatically. Then I try to restart and shutdown my computer many times but it doesn't do anything (no message, its like i didn't even click the restart or shut down button) Then it gets more worse by firefox browser not opening and start menu saved shortcuts disappeared. So I had no choice but to manually power off the computer by unplugging it and when it is back on EVERYTHING IS BACK TO NORMAL! But just to be caution, I deleted all temporary internet files and cache. Then, I scanned my computer with kaspersky internet security but it didn't find anything. Also checked windows task manager for any suspicious process running and googling it and didn't find anything suspious. I even tried hijackthis tool but it didn't find anything also. I don't know whats the problem is since after 10-11 hours again (not continous work since I only surf online, read ebooks, sell on ebay, watch vidoes and nothing like that needs a lot of power like playing games, photoshop, making movies, etc) it does the same thing over in the same pathern. Please ADVISE on what I should do since I do not want to damage/erase all the MEMORABLE documents, photos and other things My family deeply cherish. We will be waiting on anything that can remedy our situation!

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i have toshiba satellite 1400-s151