PC shuts down during boot

An old PC (PII 233 Mhz) does not boot up properly. It beeps, start to boot, but it shuts itself down about a minute. The monitor claims it gets no signal from PC. (This happened some time ago, but when the PC had started and windows was up and running the screen started up)
I suspect the powersupply is not function properly or the grafic card. Any suggestion?