Need a bit of help with M17X R3 6990M

Hey

A few days ago my cousin gave me this "piece of trash" of computer,that's what he called it.
Anyways i have been trying it out and there are 2 main problems that i don't know what's causing them.

The first one is...

-I don't get the performance i should be getting.
For example i should be able to play at least SWTOR on Max or High settings and i'm getting 10-20 fps at Max settings.The only way i can play SWTOR is if i change all the settting to lowest.
I also seem to get a lot of fps lag in League of Legends with max settings so there is obviously something wrong.

The other problem is...

-I get a 5-6 seconds lag spikes on all my games,it can drop from 60 fps to 15 fps and then it goes back to normal.However this fixes it whenever i disconnect the AC adapter/battery and as soon as i plug in the AC adapter/battery to my computer,it starts to lag again,if i disconnect it then there is no lag.

My specs are :

M17X R3
Intel(R) Core(TM) I7-2630qm [email protected] GHz
RAM 6.00GB
Windows 7 64 bits
BIOS A12
Catalyst version 13.1

English is not my main language so i hope you could understand what i meant
Thanks.

 

I would check and clean out your fans. It sounds like the GPU is throttling so clearing the fans should help.

 

Could be a power port issue but seems more likely it's overheating. I would do as suggested above and make sure the heatsinks and fans are clean. If that doesn't help then take the heatsinks off and repaste them. After you've done that stuff then start worrying about if it's a more serious problem but it's generally best to start with the simple cheap options first and work your way up unless you have a good idea of what the actual problem is.