Imho it's either the RAM or the HD, had the same problem a couple of years ago had to restart my pc like 6/7 times in a row to make it work.
If u have access to them try starting it with 1 RAM at the time and see if it's that.
If it's not the RAM then 99% it's the HD.
Solutions : buy new HD/RAM or if it's an old PC buy a new one xD