Hi everybody!

Recently, the following problem has appeared: if my computer works for several hours then it gets into the state in which it doesn't respond to mice/keyboard manipulations. In this state, the monitor is switched off and the computer itself continues to work (fans spinning and LEDs shining). Only Reset button helps.

The problem more often appears when the computer is in the idle state: programs either are not actively working (when a bittorrent client is not downloading and uploading, for example) or not launched at all.
In the "Power Options" menu, High Performance mode is chosen (Sleep function is disabled); "turn off the display" is set to 5 min, other options haven't been changed.In BIOS S.M.A.R.T. and XMP (extreme memory profile) are enabled, other options haven't been changed.

RAM was tested several times using memtest86+ (about 12 hrs) and default Windows memory diagnostic tool -- errors weren't discovered. Stability test was performed using prime95 (12 hrs in each of three modes), simultaneously, I launched FurMark for a short period of time -- errors weren't discovered. S.M.A.R.T. is normal in both hard drives. BIOS is updated to the latest version; and I tried to reset it to defaults too. I use latest drives (before that, previous drivers were used), it didn't help either.

Computer specs:
1) APU -- AMD A10-7860K;
2) MB -- Asrock A88M-G/3.1 (BIOS v. 1.40);
3) RAM -- Crucial Ballistix Tactical (4 x 4GB) DDR3-1866 BLT2CP4G3D1869DT1TX0CEU (in the approved vendor list);
4) PSU -- Chieftec SFX-250VS (250W);
5) SSD -- Crucial M550 256Gb (firmware updated);
6) HDD -- Toshiba E300 2Tb;
7) OS -- Windows 7 x64 Pro SP1.

Please help!