Upgrading would obviously be the most recommended.. What makes you think that your motherboard is failing.?
We paid a guy this morning to come out as for the last 6 months the computer will either boot up or I will just get the black screen with no signal on the monitor, and then sometimes whilst working it will just turn off. He said the motherboard is failing
The safest approach would be to get a good quality PSU first.. I call it safe because even if the PSU does not turns out to be the actual problem, you'll be better served with your purchase for a long time.. Either of the Corsair CX 400 or the VX 450 should be enough to handle your rig..