Random freezes - USB ports failing

Hi guys, I figured this was the right place to post this.

I built a new PC around 18 months ago, and on the whole things were good.

However, as of the last week or so, I've been having some problems. Every now and again the computer will freeze - fans are still running and the screen looks normal. However the mouse won't move and it soon becomes apparent that it has frozen, the only fix being to force it off.

another problem, again within the last few weeks is my USB ports apparently failing. It started happening occasionally however this morning it has gotten to the point where none of the back ports work - when my illuminated keyboard is plugged in it just flashes randomly. Strangely, the 2 USBs on the top of the case do still work allowing me use of a wireless adapter and mouse (but no keyboard - I'm having to type this using the on-screen keyboard).

My setup is as follows:

intel i7 - 2600K
ATI Radeon HD 6950
Gigabyte Z68 MOBO
OCZ verrex 3 SSD
2 other HDDs

I've run Malwarebyte to no avail and the same is true when the AV from Security Essentials was used.

My voltages are as follows (I saw someone post these before so I thought it might help...):

VCORE 1.04V
+3.3V 3V
+5V 4.88V
+12V 8.88V

It's maybe worth mentioning (or not) that when I upgraded, I kept the case and the PSU.

If any more info is needed, let me know.

Still looking for some help - main issue is the USB ports failing.