Plagued with problems

Recently I discovered my younger siblings penchant for pornography, on MY computer. As a result, a host of nasty problems have erupted. As I am a dunce with all this technical stuff (gamer here) I will show you the system specs of my computer that I can find.

Windows XP Home Edition
Version 2002
Service Pack 3

Intel Core 2 Duo CPU
E6750 @ 2.66 GHz
2.67 GHz , 2.00 GB RAM

Alright lets start listing off problems.

1) Upon starting my computer, I get the typical XP loading screen, however, sometimes the login screen does not appear, and I am stuck with a black screen and a mouse arrow.

2)Once I log in, there is a 50/50 chance my computer will simply freeze. Also, whenever I log in, a popup at the bottom left corner tells me that "userinit.exe" is corrupt and I must use the chkdsk function (which does not help). Every time i use any sort of .exe, the same mesage appears "firefox.exe" etc.

3)When I play ANY game which consumes the whole screen (an FPS shooter for example) I have roughly 30-45 minutes of playtime before I receive an error message saying "Services and Controller App must close ". It then initiates a system shutdown on a 1 minute timer.

4) Whenever I try to install an anti virus program such as Norton, i get an error message saying that there is another installation in progress, which there is not.

5)The start-up freeze sees to only be resolved if i bring up the task manager and end the process "msiexec.exe "

6)Any form of instant message service simply freezes upon start-up.

7)Random freezes/computer restarts.

Any ideas? Or should I save myself the trouble and take this thing to the local computer shop now?

Oh, and I don't have my original Windows XP install CD, woooooo

 

Unfortunately, neither of the links of those mirrors works. Whatever is in my computer, it is clever enough to block any and all websites which even hint at spyware removal or tech support in their name. I'm surprised I was even able to come here.

I can't even access the Windows site. Or receive automatic updates.