Well that could explain your whole problem.
No it cannot, and the amperage is not anywhere near the low side for the current system config.
The only major consumer of 12V current is that AMD X2 4200+ @ 2.2ghz, and it's using less than 9A, probably closer to 5A when bottlenecked by the video in a game, unless it was such a horrible overclocker that the voltage had to be pushed to extremes.
The video card is very miserly, using 2A or less, because it's a 7600GS not even voltmodded or o'c past GT levels.
Remaining significant 12V consumers are the hard drives, but only upon system power-on when they're all spinning up. Suppose he had 4 hard drives, which most people don't but let's suppose it anyway. Typical current about 500mA per, if/when they're all spinning (which isn't necessary either for gaming but again let's just suppose they are since we're trying to find a peak momentary current requirement), so 2A total at the point where either the CPU or video card could be maxed out.
It's doubtful the optical drive is spinning or that fans are using significant addt'l current but let's give them 1A anyway.
The math.
9 + 2 + 2 + 1 = 14A maximum PEAK power.
Typical power is going to be even lower.
Any honestly rated, decent quality PSU claiming 14A @ 12V should run that system fine for many years.
On the other hand, some 2900 would require a PSU with more than 28A on 12V rail.