File 9 Dirty?

Ok i have windows XP media center edition and about a week ago my computer start randomly restarting even while i was in the middle of something. I have no clue what was causing this and after every time i would run Norton virus scan and it came up with nothing. As time went by it started doing it more often and when it did it once it would do it quite often until i turned off my computer and let it sit for a couple of minutes. Finely it started doing it one night and i tried running virus scans and it restarted before it even got close to finishing the scan. While it was booting back up it restarted again and then in the second boot up it again restarted. After that i got an error message saying that File/Folder(not sure) 9 was dirty and it was doing step 1 of 3 to fix it(something to that effect)... I'm not exactly sure of what it said (sorry). All i know is it began scanning my computer and then it got to step 2 and began deleting files on my computer. Then on step 3 i wrote down exactly what it said "Replacing invalid security ID with default security ID for file 1~160k+. then my computer rebooted and when i got to my desktop from what i can tell i believe all my system data(or most of it) was deleted. Internet won't come up, system restore wont work(it says system restore cant protect your computer, please restart and try system restore again), and my speakers and such don't work. When i received my computer when i first bought it i received no system disks and i have no clue what to do. I'm not sure if all i need is the system disks to fix it or what. One other thing is that all my files, programs, and settings were still there such as background, games, etc. Another strange think i came across is that it will allow me to play online games but when i pull up internet explorer it blinks up then closes before i see a single thing. I would really appreciate some help and I'm sorry for the vague details i can provide  =/