The most power hungry Pentium 4 chip that I know of consumes up to 140 W.
The most power hungry graphics cards can consume up to about 150 W.
Then there's hard disks, USB devices, optical drives, the mainboard itself. Those components are not as power hungry as a CPU or graphics card, but they sure need power.
For a Pentium 4 system, a 300 W PSU is a bare minimum. And the quality of the PSU is very important too - a low quality cheap 400 W PSU delivers less power than a good quality 300 W PSU!

Did those "C++ error" messages show up AFTER you installed the new memory? In that case, it's rather likely that one of the memory sticks is bad. You can test that by setting the Quick POST option in the BIOS set up to Disabled - at the next reboot the system will test your memory chips before even attempting to start the operating system. If there's a bad memory module, the POST (Power On Self Test) will most probably discover it.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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