Sounds like hardware offhand. I'll suggest two programs to run to see if anything is reported as bad but before doing that, I will also suggest checking all your cables inside to make sure one (or more) hasn't become loose. First is Memtest86 the second, Seatools. Both are free programs. Run Memtest for a few passes (three to five) to check your ram's function, then run Seatools to check the health of your HDD(s).
I'm guessing between the two, you may find your issue