Dimension 3000 blank screen wont pass start up

hello

first time newbie alan here.

i have a dell dimension 3000 which has served me well without fault for years but.........

screen whent blank yesterday .tried switching computer off etc etc ,all i can get to happen is the computer starts up the screen comes on for approx 5 seconds but doesnt move on to desktop but goes a very dark black ,i thought it may be the monitor so tried the monitor on my work pc and it operates perfectly.

tried unplugging everything on tower etc but screen still wont pass the initial intel inside message.

will i need to install all disks as when i first bought it ?? or does it need to be recovered by a shop ?

any help gratefully recieved as i have all my business diary etc on it

many thanks alan