What the HELL is wrong with my computer?

It sounds like a virus. If you can, open task manager, and see what is hogging the CPU and RAM, if it is not a name you recognize it is probably a virus, and you should use your other computer to put an antivirus software on a flash drive (so it doesnt take forever to get to!) and run it on your slowed down computer. there are several free anti-virus programs, look around on google to find one that you like.