Turns on but won't boot

[Bones1669]

Last night I was on my computer and the the phone rang, when I came back my monitor had fell asleep. When I went to move the mouse to wake it up...it did nothing, black screen still. I changed the mouse and still no change. Infact, light does not come on on the mouse.
I shut the computer off and when I went to reboot it, it turned on but the monitor remained black. No POST screen....nothing, just black.
The light on front of the computer stays red, does not ever go green. The light on my cd drive doesn't do anything either, doesnt even flicker.
I have tried a new mouse, other monitor...I have no clue.
I am running XP on a P4 M900 with 1GB ram and my hard drive I think is 250.

I know it's likely no quick fix, but I sure hope its not the motherboard.
Any suggestions wopuld be greatly appreciated.

Thanks in advance.

[Greg4057]

Did you hear any beep? My MOBO user guide has a table showing start up beeps and what they mean, like keyboard detected/not detected, VGA detected, etc...
If you're hearing any beeps you might want to find out what they signify
I am by no means an expert but I did my first computer build and start up over the last two days, and had some boot up problems to deal with. Your situation is obviously different

[Bones1669]

I hear no beeps...just fans.

[Greg4057]

That doesn't sound good - maybe it wouldn't hurt to check the simple things like power supply connections to the MOBO

[Big_Daddy]

Swap the memory in and out. You may have lost a memory module

[Bones1669]

Thanks Greg and Big Daddy for replies.
I have checked the connections, as far the memory I have none to replace it.
If it was a good chance of being the memory I wouldn't mind spending the money on it. I will make some calls see if I cant round some up cheap.
Thanks again.