Help With My Old Laptop Video Card Problem

i have my old laptop Dell Inspiron 6400 Core 2 duo @ 2ghz and a Ati Mobility Radeon x1400

My problem is When i play games like pcsx2 or any games and watching Bluray movie

the memory clock is going down and down until it reach only 135mhz something so when i play games but the gpu clock is stable only the memory clock is going down and down so i get hang when playing games and watching movie so what i do is when the memory clock is going down until it reach to 135mhz something i use powerstrip to set the default clock again but sometimes it will hang and crush the laptop it will produce some lines and hang so i need to restart my laptop what do you think my problem and how can i fix it thanks  )))