9gb Ram installed. 7 Gb shown as installed, 6.1gb available. Windows 8

We still need to know if you have a 32 or 64 bit Windows 7.
If you press the Windows key and the Pause key it will tell you their.

Their are many motherboards when I Google ECS p45 t Black Serie. Could you point us at the site that has your exact motherboard and its specs.
You also should download the motherboard manual if you don't already have one. A proper motherboard manual is a absolute necessity when choosing hardware.
These steps you are being guided through are not because I'm lazy. They are steps that one must know for now and in the future to work with hardware for computers.
Please get back with the information.

The information on your motherboard is all over the place. It is a duel channel with 3 ram slots.
Your cpu specs LGA775, RAM 1333.
If it was my computer I would install 4 sticks 2 gig each of DDR-2 667 spd ram. 8 gigs of ram will be more than enough for that system.
Her is a site that gives some good information on your motherboard that might help.

ECS P45T-A Intel P45 Chipset Motherboard Review | Features and Specifications

I think their is a good chance that having mismatched ram and what slot you are installing them in is causing your problem. If you install 4 sticks of proper matched ram that should take care of the problem.
Please remember never install ram in slots you think they should go in. Only install them with the method given in the motherboard manual.
Your older system would work quiet well with 4 gigs of ram. Two sticks of 2 gigs, but they must be installed in the proper slots as per the manual.
If that was my computer I also would not over clock it.
Very little to be gained except more heat which you don't want.
If you have anymore question, please ask.

Well the reason I am trying to get to 16gbs is simple. I want to use the pc to edit videos. I use vegas hd 11 and 12 and I suffer. Editing is tedious and slow. Rendering? that should even be forgotten. That's just off cellphone videos from my blackberry 9550!

I need the ram. An here in South Africa A pc like yours or Lady Fitzgerald's costs like R20 000 or more! I'm a student who gets R800 a month as an allowance. The cost of such a machine is 7 to 8 times a monthly minimum wage salary! Ram on the "old" machine is my only option

The current exchange rate is like 9.1 - 9.5 to the dollar