Windows XP Pro 64-bit intermittantly wont come out...

Question

My PC was running sweet from new and I used to be able to press the 'Sleep' button on the keyboard, it closed down and then wakened when I moved the mouse. But recently it wont come out of the standby / suspend mode and just lets the monitor light flash. I then have to reboot. The PC actually must have crashed as the Cap Lock will not go on and the monitor screen just remains black

Any help appreciated as I've searched the net but can't get a solution

Stephen