|It's tough to make a diagnosis when you don't list any of your system specs. Some CPUs are more prone to overheating than others...the P4 is one example. When it reaches a certain "trigger temp", it will force a shutdown to prevent a burn out. Since it's happening so quickly, it would seem your CPU heatsink/fan is either totally dust-clogged, the fan isn't working, or the heatsink has come loose from it's mounting.|
Another possibility is the PSU you bought isn't up to the task. Once again, it's hard to make a recommendation when no system specs are listed but you *should* have gotten at least a 400W unit with at least 25-30A on a single +12v rail...or if it's a multi +12v rail design, each +12v should have 18-20A. It should be a reputable brand name unit & should have cost roughly $50 +/-. If you based your purchase solely on wattage, didin't pay any attention to amperage specs & paid closer to $20 than $50, it's very possible the PSU is inadequate.
Post your specs!