Long beeping sound when I start computer

Hey there everyone, First of all if this is the wrong category I apologize and please feel free to move it to where it belongs.

Anyway, I have an old desktop computer with a Rhombus motherboard and an Intel Celeron processor 2.80 ghz, 1 GB Ram 2*512 and a 500 GB HDD running windows 7, I've had it for about 8 years now, No serious problems until today.

So this morning I came to turn it on, everything appears to start correctly, But there is no display and all I get is a Long Beep sound, It sort of goes on for a while, stops then does it again the same way, stops, and on and on it goes.

So I've tried doing basically every thing that can be done on it, from cleaning and checking the RAM, Removing and re-seating the video card, trying the built in display, Fiddling with the Jumpers to stripping the board clean and starting it.

And nothing, No matter what I do I just keep getting the same annoying beep with no display or keyboard lights or anything.

Can anyone help me with this? Because I'm really happy with my Machine, its never given me any serious problems until today and I don't really want to spend 300+ dollars upgrading it unless necessary.