HP Pavilion 400-034 slimline no video display.

[blfuller]

My Pavilion 400-034 suddenly has no video output, also It seems that the computer is not booting properly.  I press the power button and all fans come on.  The CPU fan comes on at a high speed then slows down.  Power light is on, power supply light is green.  When powered up the CD-ROM light comes on and drive spins and the hard drive light flashes a couple of times.

I have replaced the battery and reset the CMOS several times to no avail.  Pulled the hard drive and checked it on another machine and it seems to be working as it can be accessed.

This machine had a video card installed in it and the on board card was disabled and the same no video issue was present.  I removed the video card and reset the CMOS and neither on board ports has any output.  Monitor is fine and cables are fine.  RAM was pulled and tried in different slots, and different RAM was tried as well with the same results.  There are no beeps of any kind on startup.

I have searched on the HP site for any troubleshooting tips and tried them and nothing has worked.  Any suggestions would be appreciate

[WAWood]

@blfuller 

The LED only means the motherboard is drawing power although the other peripherals also appear to be powering up.  So, it's unlikely it is a total motherboard failure.

Some older PCs have their video set in the BIOS manually, and if the video card fails, you can not then get back into the BIOS to reset it so the onboard video works.  But, you said you reset the CMOS -- but were you able to go into the BIOS settings and reset them to default values?

If you CAN, to find out the problem, you would need to be able run hardware diagnostics by pressing the Esc key repeatedly and then, when the HP Startup Menu appears, select Diagnostics (usually F2) and let it run.