I don't leave my pc on all the time but more recently have had problems with random freezes. It tends to happen if I don't use my pc for a while(half hour or so) then it freezes. Upon reboot, it says no hard disk found. I turn it off for a couple of mins then all is well when I turn it back on. When pc is left idle, there are no big progs running, only stuff like zone alarm etc. The temps(as reported by motherboard monitor) seem ok and don't normally rise above 50deg or so when idle(cpu temp).
What can be causing this?