First time OCing

So I haven't messed with OC before but wish to get a little more out of my rig before I have to buy a new one. I purchased this one a little over a year ago, non-custom built. Here are my specs:

CPU: AMD A6-3620 APU with Radeon(tm) HD Graphics
Ram: 8GB DDR3 SDRAM
Gpu: Nvidia Geforce Gtx 550 Ti 1GB DDR5

OS: Windows 7

So I started out by researching OCing via the Bios because most people say its the best way, but after some digging I was told my BIOS won't allow it (I have non of the required settings available in my BIOS)

So then I was recommended to use AMD Overdrive, where as it looked promising I have ran into some problems it seems. In a first-person-shooter I play I can get without OC a FPS of 120-150. Now, when I OC my processor to a 3500Mhz instead of the default running 2300, I can achieve upwards of 150-180 FPS. But then comes the problem every ~30 seconds my FPS will drop to ~90 and I notice my clock speed dropping to a range of 1900-2400. I assume this is AMD's way of controlling their hardware as to not allow it to over heat. So my question is, is there a way to force it to run at a desired speed that I set so it will never drop lower than that? Any help would be great, thanks!

Damein, welcome to the forums. Have you done any stability testing on your overclock and have you checked what your temperatures are under load?

Damien, welcome. Please tell us more about your system: Make and model of motherboard, make and speed of ram, make and model of CPU cooler, make and wattage of PSU, make and model of case. How many intake and how many exhaust fans do you have and how large are they? 120mm? Good case ventilation is critical to keep temps down and preventing problems such as you describe.

Also, please download and install these three programs we depend on heavily around here to help us in the overclocking process: CPU-z, HWMonitor, and Prime95.