Dimension L1000R dell desktop?

all right my friend recently got a old dell dimension L1000R, hes trying to hook it up to his HD TV. we hooked it up all right but when we turned it on alls we got was a random beeping noise from the PC. the TV showed a message that says "no RGB connection deteced powering off". the thing is weve hooked up his labtop to his PC just fine and this has never happend. can any 1 help.