It sounds like the primary issue is that the system is locking up. When this lockup occurs, you get the dreadful audio loop and the graphics are shutting off (causing the monitor to go to standby mode).

I'd say that your motherboard's hardware monitor is doing its job and doing it well. What it is telling you is that the voltage supplied on the +12V rail is too low. This type of problem can cause many problems from system lockups, boot failures, and component damage.

I recommend that you replace your power supply with a compatible one. If you are not sure how to check for a compatible power supply, take your entire machine to a local shop that you trust (try to find a small shop since the big name guys (Best Buy, Circuit City, etc) usually employ kids that know next to nothing about computer components) and ask them what type you need to replace it with.