FPS dramatically fluctuates when gaming on Inspiron e1505

Hi guys, I posted this in the Gaming section, but I wanted to put it here to see if I could get some more help, and if anyone else was experiencing this problem as well. I got my Inspiron e1505 laptop last summer. It's worked great until a couple months ago. When I start playing games (normally World of Warcraft), sometimes the screen will blink, and I will lose about 20-30 fps. After a period of 5-15 minutes, the screen will blink again, and everything will be back to normal. This screen blinking continues for the entire time I play and it's getting annoying. I only play a few games, but this mainly happens when I play World of Warcraft, but not when I type essays or surf the web. I have a 1.73 GHz Duo Core processor and 2 GB of RAM. OS is Vista. If anyone knows what the problem is, please help me out.

Also, something that I recently noticed was that when I pull out the power cord out during the time my computer suffers from the performance loss after the screen blink, my fps does not go down any farther. Before this problem, if I pulled out my power cord when I was playing WoW I would experience a large fps dip (I think this is normal) similar to what happens after my screen blinks. I'm not sure if this is related in anyway, but I just wanted to throw this out there. Possibly the laptop is not using the power correctly or something?