System Boot Problem

Client says after using system for a while it froze and he used cntrl-alt del to exit
The next morning he tried booting and sys. would not boot,this is after system has been running,I am thinking partially it is user error.

The other part is the problem ,why system fails to boot
Any ideas on this would be helpful
TIA
System Configuration
ECS motherboard P4
Via chip set
Intel CPU 2.8GHZ/533FSB
256k memory