We have an XPS 435MT (runs Vista) that occasionally doesn't power up.

It will be working fine when suddenly, the mouse will not work, the clock stops, you can't do a ctrl-alt-del to access processes.

After you shut down, the machine will not turn on.  The power light flashes amber if you hold the power button in but it will not power up.

If we leave the machine sit for a day, it will then power up.

Appears to running fine now but this has happened several times.

Any clue as to what might be the problem?

Thanks in advance for any help.

R. Cooper