The best thing u can do to check the problem is this.....
Insert ur RAM on some other PC (make sure that da speed matches) & see whether it is detected....If it gets detected then nothings wrong with the RAM module...
Alternatively, get some other RAM module from a friends PC & try it on ur mobo (again make sure that the speed matches)......If it gets detected, then u can rule out that ur memory slot is working perfectly....
And unfortunately, if both these things fail......time to take it to da doc....
I had done this thing a couple of years back & was successful in detecting a faulty memory slot...