If the cleanup solves the problem, you're set (and replacing the thermal pad/compound on both the CPU and GPU is a very good idea from the other reply).  If not, the GPU card will likely need to be replaced.  Carefully compare the cost of a card (if you can still find one) with that of a complete used system.  You'll then have a complete set of replacement parts ready for future failures.  An entire working system of this age can likely be purchased for $30 or less.  
I have been using a Dell Inspiron 9400 laptop with Windows 7 during the last three years without a lot of trouble. Yesterday, while playing a casual game on it I got a blue screen with the memory parity and system halt errors. Since then I have not been able to load Windows completely. Yesterday I got flashing lights for Mayus and Return as error indicators. Other times those lights were off. Num Lock light was always on. I could see something in the screen only once. Today I was able to start up once again and I tried the Diagnostics. I got only a warning for LCD connection. I saw vertical strips and artifacts on system screens but not in Windows loading screen. After this screen I get the blue screen again and the computer stops working. Thank you in advance.
Memory parity error and system halt on Windows start up