PowerEdge 2650

i really need some help with that dell machine that i have.i install 4g of memory but once i turn it on it did tell me memory had been chance so now i'm trying to install server 2008 it started going with the precess and than it told me that i have 256 memory i cant instal the server 2008 i restart the computer one more time once it get the the point for me to hit f1 for it to start it show me the its limited with 256 of memory please help me i dont know what to do its a project i have to get ready for class thank you my email is Email id removed per privacy policy>