Someone please help me. And quick.

Yesterday I received the dreaded BSOD. My computer stopped altogether and restarted itself. Later, my Firefox and a few game programs would not work. Nothing to faze me yet. I ran AVG, Ad-Aware, and Symantec Antivirus, and nothing was wrong.

Today, I BSODed again. My Windows Live Messenger would encounter an error every time I opened it. Same with Windows Messenger. Dr. Watson would always encounter errors, Explorer.exe was shutting down and restarting every few minutes.

I restarted the computer. Things were well until my computer restarted itself again. I tried to run more virus scans, but AVG has ceased to work. I want to download Windows Defender but I can't - the authenticize thing doesn't work for me.

I don't know what to do - something is eating my computer from the inside out and I am powerless to stop it! What should I do?!