My ram became slow suddnly

So here's the story, i was doing a physical clean up on my SYSTEM UNIT and after dusting the mobo and fans and turning it on, it always shuts down around after 8 mins. fixed it by reconnecting everythng properly. then the problem was fixed. after that my 2 sticks of 2 gig DD3 RAM became slow and only runs 2gig of it. i tried cleaning it and rubbing pencil earaser on it. and yet its still 2gig. what else can i do? btw its age is like 6 years already. my whole UNIT.. LOL