Suddenly and for no apparent reason, I cannot boot into my Windows 7 PC. I am running Windows 7 Home Premium 64-bit dual boot with Linux Ubuntu. On boot up most of the time I cannot even get to the GRUB boot loader. I just get a blank screen, sometimes a blinking cursor up in the left corner. I cannot boot from the Windows 7 install DVD. It starts to load windows files then freezes. I have downloaded and burned about half a dozen "Rescue CD" iso images, from AVG to Avir to Norton to Paragon Rescue Kit, etc., etc. -- all to no avail! Either they won't boot at all or they freeze during the process. I even created a couple of bootable rescue USB flash drives. Nothing works!!! Once or twice I managed to actually start a virus scan with the AVG Rescue disk, but then the scan aborted before it could even get going. It's like something keeps killing the scan. I can't even get into my BIOS! It just freezes when I hit the F10 key. What the heck is going on and how can I fix this? Is this some really nasty boot sector virus or perhaps a hardware failure? I just replaced the HDD a few weeks ago, so I don't think it could be that. Any and all ideas GREATLY appreciated!