Monitor message "no video"

Remove the NIC and see if the problem goes away.

If so, try a different slot on the motherboard. Might be a hardware conflict.

Pulled out the NIC and still "no video".

It's on board and I already checked all cards, connections, etc.

Is the "no video" message occuring as soon as you reboot and you do not see any POST message, or do you see this right before Windows starts up?  If you don't see a POST message and it was working before installing the NIC, something got unseated, disconnected, or suffered a static electricity malfunction.   Your power supply may have also died between power-ons, which you can test by swapping it out.

If the message comes on after starting Windows, you have a Windows driver problem, and you may need to boot into safe mode and delete the video driver and reinstall on reboot.

Try a different NIC Card.  Sounds to me that the NIC is keeping the moboard from running its POST.  

Try to Reset the BIOS via the jumpers.  See if that clears the bios and make the computer boot again, then try a different NIC.

Thanks all for your help.  The "no video" comes up after reboot and after I have turned monitor off, then on again.  Otherwise it just appears asleep, no clicking/scrolling makes a difference.  I have taken out the new NIC and put back the old NIC.  Several times.  I checked every connection inside and out.  Could it be the video card?  Thought it might be going out a few weeks ago, put on a new monitor and that solved the greenish desktop.

The way to test that theory is to try another video card - perhaps "borrow" one from another computer?

try booting into safe mode to see if it can load default drivers (what o/s?)

Okay, boy, have I learned alot!  The computer has an integrated video card; does this mean the motherboard itself is fried?  Can/should I replace that?  I put in a new AGP (?) video card, GForce FX, and got same "no video" message when booting up.

I think it's the motherboard, will just retire the machine till I can replace that, if it's worth bothering with.  Any ideas on that?

What's the spec on the existing machine?

If it's a prebuilt (Dell, Compaq, etc..) your options may be limited.

If it's a custom, give us an idea of what is in it.

Oops, just saw you said HP in the original question. What's the model number, etc?

Pavillion a300n.  It has a 2.6 processor which has always (in 2 1/2 years) run very slowly.  

On these proprietary systems, it's not always easy (or sometimes not even possible) to upgrade them.

What you could do (what I would do) is salvage the Processor, memory & hard disks out of the old pavillion and add in your wireless NIC, a new case, motherboard, powersupply & video card and have a fairly decent system.

These proprietary boxes are a real pain at times.

Sounds like it (the pain I mean!).  Think I will do that - but not any time too soon - have had enough of this machine, and the other one with the missing CD drives (fixed) and setting up a new one........sure wish I got paid!  ha