Computer restarts for no reason; need some help please!?

Ok guys bare with me when it comes to pc's I am a little lost.

I had a trial run of system mechanic pro7 on my system which operated fine. I never had any problems with my system, system restarts, or anything of the sort. My trial ran out and I didn't have the money to buy it so I decided to uninstall it and go to a free antivirus and firewall. Before I uninstalled System Mechanic I downloaded the firewall and antivirus but I did NOT install them I just saved them to my desktop.

I went to my control panel and click the remove button and it said that it could not remove it. Some things did remove but others would not. So at first I ended up blocking my IP address with trying to remove this stupid program, but I got that fixed. It said that it was not installed so I installed the new antivirus and firewall but when I rebooted the system mechanic loaded along with the new anti and firewall that I just installed, but I got an error saying that real time setting could not be loaded. I downloaded REVO, an uninstaller program, and seemed to get rid of it the System Mechanic didn't load, and I am thinking this is great.

Now I am faced with a new problem my system just reboots whenever it likes. My screen just goes black and it goes through the normal start up process. There are no error messages just a normal reboot. Another thing is when I click start and then restart my system just sits there I can't initiate a manual reboot.

There is no way that I can afford a new pc right now, I am getting ready to move, and I need every penny so if you can hell me I would really appreciate it. Oh and please talk to me like I am two because PC lingo is not a strong point with me I do well to be able to remember "msconfig". Thank you so much for your answers I really need some help on this one and I don't know anyone that I can turn to.