Solved Sleep Mode Stops To Work Well, PC is Dead After Wake Up

I use my computer as HTPC, so I always use sleep mode. In last few days it wakes up through the nights and doesn’t react for anything, so I need to shut it down by starter button. Then, I have to reset my BIOS, because if not, my PC starts, but doesn’t react for anything too.
I’m testing sleep mode now and I can see that after two-three times, PC starts waking up immediately after I try to sleep it and is totally dead as after night wakes.
Last night, I’ve just shut my PC down and everything was good, but it works for years as HTPC, so sleep mode is much more comfortable.
Do you have any ideas?