I have recently built a new computer and when I turn my computer on everything seems to be running, but the monitor stays black and the LED light on the monitor stays yellow (or for other monitors blinking, you should know what I mean). How can I get my monitor to notice my computer running!

I am using...
Pentium 4 3.0 GHz
PCChips Motherboard M955G
Rosewill 512 Mb RAM (Tested OK)
ExcelStor HDD 40Gb (Tested OK)
400 Watt Power Supply (Tested OK)
floppy drive
CD-Combo drive
Sapphire Radeon 9250 (Tested OK)
2 Fans + CPU Fan + Power Supply Fan (All run when turned on)

Hopefully you guys can help me out here.

Firsty, check the pins in the monitor plug to see if any are bent or broken. If there is no problem there, then you will need to check that the graphics card is in securely and that all other cards and ram are secure in their slots. If it still wont work, you need to check that the power supply is running properly, if you disconnect it from your mobo you can test it by shorting the GREEN wire to any of the blacks with a bit of wire. Be careful doing this as it can damage the power supply if done to often.

Let me know if you need anymore help. Rik.

The motherboard has intergrated video, so the video card doesn't really matter. I use the same monitor that I am using to type this message, so that is OK. The computer that I built does turn on, so the power supply works. Any other ideas?

Basically, if it all powers up but there is no display output, it means that something is not starting correctly. If you can, you need to check every removable component with your other pc to narrow the cause down. Another thing to try is to remole the reset switch connector from the mobo ( I once had a case where it had been wired incorrectly. Also, it doesnt always mean the psu is working properly, even if is seems to power up. You may need to check all the different voltages on it. If you have a volt meter I can help you do that.

OK, I have tested all the devices before and they do all work, but I can't test the P4. This is the first computer that will use a P4 that I am building. let me tried the reset switch remove idea and get back to you later. I must go to work soon.

I took out the processor and turned the computer on, just to see what happens. It does the same thing! On my motherboard there is an ATX power connector and a PJ connector. If I wouldn't connect the PJ connector, what would happen?

The PJ connector is extra voltage supplies for the processor mostly, so with it disconnected you will probably get it to power up but not work.
Just a thought,do you have a speaker connected and does it bleep? Or does your mobo have any status display l.e.d's (as mine has).

No, there are no beeps at the beginning. I have status lights (like HDD and Power lights on the front) and none of them light up when the power is turned on. I wondered about the PJ connector because a wire came out of the connector before, but i soldered it back in and voltage does go through it. Maybe I have a jumper wrong or something. Any ideas of what I can do yet?

You could try taking the mobo out of the case, place on the antistatic bag it came in and powering it up like that. If that works then there is a short to the case somewhere.

When you say a short in the case, what do you mean? First time making a computer so I want to know everything.

Three things i have seen in the past are.
1- a brass spacer was touching the end of a component on the underside of the mobo.
2- a brass spacer in the wrong place shorting the underside of a ram slot.
3- the head of a screw shorting 2 pins on an ic.

P.S. i have built many pc's and helped friends with theirs so ive seen a few.

Hope that helps. Rik.