I am going to go ahead and share my hypothesis.
First off, some quick questions...
~Have you installed any new hardware, replaced some old parts?
~How long has this been happening, since the PC was purchased, or is it a new experience?
~Have you done any sort of benchmarking to determine a baseline of performance?
~Are you overclocked in any way?
~OS (operating system)?
~Why are you disabling CCC (Catalyst Control Center)?
Without these answered correctly, it is very difficult to ascertain knowledge of the problem at it's root cause. There could be a concert of issues plaguing the system, it is best to isolate with the basics.
My hypothesis is this. Hidden in
this link you will find a glint of a possibility that may solve your problem outright or may just do absolutely nothing. This is called the "Windows System Assessment Tool (WinSAT)". Quoting the article it reads...
~Open a command prompt, type "winsat formal -restart clean" (without the quotes)
It will then begin a series of tests and evaluations for your hardware. What I am guessing here is that you bought the ATI radeon HD 6990 as an aftermarket GPU. My best guess is that HP doesn't put that quality of a card in its systems. I could be wrong about this but it will certainly not do any harm to you PC by attempting it.
Also if you spend as much time as I did reading that post in the link, you will gain a wealth of knowledge. Beware some of the information is slightly inaccurate, but overall its pretty much spot on when it comes to performance.
Answer the questions and we will go from there.