Various error messages installing system files/drivers.

Hi, can somebody assist me with my issue please?

I5 2500k
HD6950
8gb ddr3
asus p8p67

Various error messages installing system files/drivers:

The exact error message can vary depending on what I try to install but I always get a failed installation of graphics driver installs, direct x updates and windows updates.
An example from when I install a new steam game and the directX update begins is here: imgur: the simple image sharer

It only appears to affect system updates; games and applications install and function fine.
I am virus free and the problem appeared out of nowhere a few weeks back. The OS install is around a year old.
I have tried defrag and the disk error check scan.
I don't have a system restore from before the issue began.
Everything else within windows appears to work without issues.

Any assistance is welcome :)

Ok I did that scan and it found errors, some of which it could not repair.

I am going to try to replace the files that are damaged, which are:
SPInf.dll
winspool.drv.mui
msiexec
wet.dll.mui

Thanks for the assistance. I decided to go with a repair install in the end. The problem is now solved :)