Think I had a virus or trojan

For the past few weeks my computer would start when I pushed the button the shut right down. The only way to get around this was to unplug it and plug in again. Sometimes it took a few tries to get it back on. Other times while booting up it would freeze and then shut off instantly and it would have to be unplugged and replugged to do anything. My McCaffe that comes from my internet provider found a trojan a few weeks ago and claimed it fixed it. I had to go online and a fix I found recommended by microsoft called RegCure it had me buy. It claimed to have found a bunch of troubles and fixed them. So far it is working good. Anyone else have this trouble? I figured it was a small fee to fix than replace the tower.

Seen this type problem a few times on older machines. First off if it does not even boot to Winders it is not a virus/trojan issue, its a hardware issue. Normally random shut downs are caused by lots of debris inside of the case. I would start by opening up the case, take it outside and hit it some light compressed air. Clean it out. You would be amazed how much dust will affect a mobo.