Fps drop

Hello my name is crocodilia Im a renekton main on this game. Recently ive been having some hardware issues with my laptop. Im only able to run this game at a max of 40 fps. I used to be able to run it at 140. So something is seriously wrong. At the start of the game my fps sit at 140 but as it progresses the frames drop intil they can get no higher than 40. Its not a heating issue....I have the speccy ap that tells me how hot all the hardware is inside of my laptop and the hotest thing in there is the motherboard...which sits at 70o c. I almost feel like the gpus are switching off mid game. Here are my specs:

Model/year: alienware m17 r1 2008 pre dell Cpu: p8600 dual 2.4ghz Gpu: hd radeon 3870 (crossfire) Ram:8 gb ddr3 Hard drive: 250gb ssd sata 3

Its no super computer but it should be able to run this game perfectly. Especially with a crossfire dual gpu setup. The gpus alone should be able to run this game perfectly by themselfs.

Its an old laptop so here are the problems it has that could be related to this:

1: on start up its fails to start and goes straight to the bios beeping non stop the entire time. You have too go to exit and save changesnin the bios to get it too boot. 2: battery is bad 3: it randomly shuts off like someone pulled the cord if its just running on the power supply and not the battery 4:its been over heated a few times to the point of emergency shut down by old owners 5:power jack might be bad 6:random power fluctuations...flickering lights. 7: vista 8: screen locks up every 30 min and becomes unresponsive. I have to use ctrl ult delete to get it to unlock. 9 bios is choppy and lags 10 after taking it apart it looks like their is burn damage on the motherboard itself 11 its very old

Plz help me figure out what could be causing my fps drops. Its not over heating so dont even suggest it.