Black screen???

i have a new tower, purchased on-line last week and working fine for 1 day but today my monitor flickerd off and on. then entered sleep mode. now wont boot,just black screen with no input and no keyboard or mouse power. tried removing RAM turned on , got the beeps. tried in different slots, no change and even tried rubbing with a rubber... have i got a RAM failer, no spares and want to try and avoid return to base expensive carriage costs.
please advise with thanks