5150 won't turn on after virus

Hello, sorry I cant put any punctuation I'm trying to write this on an ipad in HTML. I have a Dell 5150 and about 2 weeks ago I put a memory stick on my computer. I formatted the memory stick successfully and gave the stick to my friend. He put a movie file on the memory stick on a MacBook pro, and I plugged the stick back into my computer. There were some hidden folders which I took no notice of, and I got the video file. I have Microsoft security essentials installed. Later that week I noticed poor performance on my computer, but thought nothing of it. One night I was watching tv, and I have a USB fingerprint reader which started flashing red for a split second as if it was powered up, despite the computer remaining off. I also noticed my card reader was also flashing intermittently. After this the computer was very slow, and I had a couple of windows blue screen errors referring to my ATI video card. I then had a few problems turning the computer, sometimes the computer would turn on but the screen would not turn on. None of the diagnostic lights were on. I tried to download new BIOS for the computer but before I could I got a blue screen error, and my computer will now no longer turn on. I can press thte power button and nothing happens, no lights flash, nothing. I know it is still alive because the light on the Ethernet cable port still turns on and off when I connect and disconnect the mains power. I am going to take out all pci and additional ram cards and retry but If that doesn't work I have no idea what to do. I think it was the memory stick that gave me the virus, because Microsoft security essentials picked it up, and said it was on an external drive. I really need help! It's 7 years old and has been restored a few times after viruses and too many programs slowing it down, but I hope this isn't he last thing. I can't quite replace a computer with an iPad!