If your system starts running reeeaalllly slow, refuses to open programs and begins shutting itself off, you should:
a. defrag the hard drive
b. call your internet service provider and your security provider and tell them what's wrong
c. mention it every time you see the person who built it but never bring it to them for diagnosis
d. wait until it's unusable and then ask if your system builder makes house calls
In this case, a casual client (I build his system but have never maintained it) did all of the above. And no, I don't know him well enough to put him on my "house call list". I made him bring the system to me.
After 5 minutes with the computer, I can tell how infected it is. 133 Trojans, 55 hijackers, 3 security shut downs (turns the anti virus off every time you boot the computer), 18 worms and 15 trackers. It was not only embedded in the registry, but in the system restore, the windows pre fetch folder and documents and settings under the name of the owner. I put three and a half hours hours into it and I still couldn't guarantee that it was 100%. It seems the owner had thought he renewed the anti virus in February. He had not. He was also not running a firewall. I think the hard drive may be permanently damaged.
I spent part of the weekend configuring his new computer. He didn't want to invest any more money in trying to bring the old one back to reliability. While I understand his thinking, that computer could have been saved if he'd brought it to me (or any geek) 3 months ago instead of trying to blame Comcast and McAfee. He could have saved himself a lot of time and trouble.
His new system is sweet. I hope he takes better care of it!