Looks like a failed hard drive. Probably a failed cluster where a part of the windows is located so that's the reason why it won't boot up. I just had a computer do the exact same thing and ended up being a failing hard drive. Try...
Does the hard drive make any unusual noises? You can still try running a hard drive test like the bootable Hitachi Fitness Test:
http://www.hitachigst.com/hdd/suppor...2_v412_b01.iso
and try memtest 86 to rule out the hard drive and...
Check out newegg for RAM prices.
A now application of thermal paste and possibly a fan replacement should do the trick. It uses a desktop cpu so it is prone to be running hot.