Windows 8 Activation Problem

A while back ago (around 2012, December) I bought a pre built Dell PC and it came pre loaded with Windows 8. In February I thought it was about time to upgrade my PC, so I bought a new MB, CPU and GPU. This reset my Windows back to trial version. I then upgraded my OS to 8.1 and only now have I thought to solve this problem as Windows has been running quite bad lately. When I'm in the Metro searching for things my CPU usage goes straight to %99. I have my old Windows Key if that helps.

(Games are crashing and stuttering horrendously.)

These problems have started to occur after upgrading my GPU from a GTX550ti to a GTX660 OC

My Specs;
CPU: Intel i3 3220 3.3GHz
GPU: Asus GTX660 OC Direct CU II
RAM: 6GB DDR3 1600MHz
HDD: Seagate Barracuda 1TB 7200RPM
OS: Windows 8.1 Trial

(I have booted in to safe, that's where I found the CPU usage problem and it seems to be the same when booting in to regular mode.)

If you have a Win 8 OEM key, that cannot be used on the new motherboard for activation, as those cannot be transferred.
You will need a retail, or new OEM system builder key.