sleep mode (no way out found)?

pc fires up then moitor says its going to sleep, screen goes blank, amber light on. the pc itself has its blue running ligt on together with the sound of the cooling fan. no responce from mouse or keyboard will get it out of sleep.warm/cold restats have no effect either cannot F8, F11, to jerk it into BIOS so do not now have a clue on what is happening, no known sleep modes have been selected. Can someone please help. homework now getting behind. Thank you