I just ran a test over at PC PitStop and on the whole my PC is working well. CPU is top 2%, RAM top 7%, Video top 11%, 3D video top 6% and then my HDD... bottom 45%.
This isn't a cheap HDD either, it's a 1TB Western Digital but it recorded the transfer rate at 48 MB/sec. I don't really know if that's good or bad, but being in the bottom 45% for a 6 month old HDD can't be good.
The only reason I ran a test was due to strange Windows freezes and slow booting, so I figure after that it might be the HDD. It does list a potential problem that my fragmentation is at 5%. I also have a partition on my HDD that I installed Windows 8 on, it has 20GB allocated and has been formatted and empty - I am not 100% sure how to remove it so just left it.
Anyway, any help would be greatly appreciated!
Edit: On another note, I did run a SMART test on it and it came back okay (this was using SpeedFan).
Edit2: Just done a test on HD Tune, did a benchmark and this is what it finished with:
The random dips look a bit alarming, but I am not really sure if I'm honest!