Few things:
1. 131 error means the ram in bank 3, the first ram, isn't working. This happens to be the first ram it checks. So you've got a 1 in 24 chance that it's actually bad, what 131 error usually means is NONE of the ram are working (and it fails at the first one it tests)
2. The startup sounds you're hearing are the sound board starting. It'll do that on it's own, even if you unplug everything else so that doesn't really mean much.
3. What your problem probably is, relates to voltage. The 4116 ram chips need amazingly 5 volts, -5 volts, AND 12 volts. So if one of those voltages is missing or not right, they won't work, and you'll get the 131 error.
So take a multimer, and check the voltages at the 4 corners of 1 of the ram chips. You should get ground on one corner, 5 on another, -5 on another, and 12 on another. If any of them are missing that's your problem.
If one of them is missing, it may be because your connection on the main board from the power supply is bad, you may have to resolder the pins, or you may have to rebuild your power supply.
Good luck!