Nagging issues w/ Asus P5KC or is it my PSU?

Current System:

Asus P5KC
320 GB WD
500 GB WD
850 OCZ Modstream PSU
Windows 7 Ultimate

It all started when I gave away my perfectly good Asus P5QL-EM to my Mum who needed a desktop built. So as an upgrade to myself or so I thought... I picked up a Used Asus P5KC seeing as it had better specs than my old one.

As soon as I swapped motherboards I started having small random problems, but I have a strange feeling my PSU may have a hand in this aswell..

Main Problems Ive encountered:

1)

I go to move or nudge my case in a certain way or angle (while its on) and the machine just dies on the spot, hitting the power button does nothing. Eventually I can get it running by randomly moving the case again or fiddling around with connections to the board. Ive tripple checked, inspected & tightened all connections, but I still get the random shutdowns from time to time but only when the machine is physically moved or jilted.

2)

After reformatting my HD after a bad virus, I noticed my external HD (2.5", uses two usb ports) not being recognized nor drawing power. You can hear the discs clicking like its having trouble spinning. Naturally I assumed that the drive had just failed, but after testing it on 3 different machines it never once gave me this problem. I reinstalled windows, all drivers and still this same external drive wont connect or draw power like it did once before. The interesting thing is I dont get any problems whatsoever with any other usb devices or drives using singe connections.

3)

Lastly, I recently had to leave town for the weekend, so I tuned off the switch on the back of my PSU just for precaution sake. A I arrived back few days later and the machine wouldn't turn on. After trying again it fired up, but this time it gave me a "Cpu fan error" !!! For now I have been getting along by doing a hard reset on the machine when this msg pops up and eventually after a few tries I get windows to boot up. Ive noticed this mostly happens early in the morning when the machine is cold, but if the system's been run recently it powers off and on normally.

Besides these nagging issues the machine usually runs fine.

** Not sure if it would help, but Im going to try and reset the cmos when I can get my hands on a E6xxx cpu, as I learned the hard way the first time this board's original bios does not support my e8400. Also Im going to have to borrow someones PSU and see if any of the symptoms change.

Any thoughts or suggestions would be appreciated

1) You should test it outside of the case to make sure that a short isn't causing that issue.

2) The external hard disk might require more current than the motherboard can provide.

3) Either the PSU or the motherbaord could cause that issue.

Wasn't the OCZ PSU still under warranty? The Seasonic is an excellent PSU.