PC struggling to boot, USB never recognized...should I get a new mobo?

About two or three days ago I made a thread about how my USB devices were disconnecting randomly: http://www.tomshardware.com/forum/ [...] w=0&nojs=0

As you can see I thought I solved the problem once I plugged my WiFi adapter into an external hub. Then the next day, the issue arose again and when I tried to use all of my USB devices with the hub the issue still wouldn't go away. Based on what the others said in that thread, my next option was to get a cheap new test PSU. So yesterday I got a new 500W Inland PSU for around $30. I installed it but it didn't solve the problem. After I installed the 500W PSU I was using my backup PS/2 mouse and keyboard but soon after they stopped working as well.

Now things are starting to get worse: I've noticed that my PC sometimes stalls when I try to boot it and I'm forced to press my restart button until it boots correctly. I also have a separate Windows 7 partition that is having the same symptoms.

Now I'm thinking my old PSU may have caused some electrical damage to my motherboard. However that may not be true: when I'm booting up the PC the BIOS has no problem picking up the PS/2 keyboard and mouse and responding to my commands. So if this WAS a hardware issue then I shouldnt be able to use them at all.

Now you can see the dilemma I am in. Can anyone offer any advice?

AMD Athlon 64 X2 3800+ 2.01GHz
DFI Infinity UltraII-M2 motherboard
2x1 GB DDR2 RAM
GeForce GT 240 512mb GDDR3
400GB Seagate HDD

A 500watt PSU for $30? Might not be a smart move! Sometimes you can get budget PSU's from quality manufacturers for $30 after MIR. Never heard of the brand you got!