psu rated in watts, old ones 200, 250 maybe 300, new ones 400, 450, 500, gaming systems 650, 700, 1000 ... depending on the parts you are trying to assemble, you may have out-stripped the capacity of the supply.
generally a pentium 1 system should have no problems with a 200 w psu... I have seen them built all the way down to 150 watts... but if you have 8 hard drives connected to the old system, you'll need more power.
in other words, list out all the pieces you're trying to make work together, as well as the wattage rating printed on your PSU label.