PC will not boot from cold

[Cheerful Dragon]

For some time my PC was on 24/7.  I switched it off at Christmas and it took several tries to get it back on.  I assumed it was just a glitch and didn't worry about it.  I left it running 24/7 for a few months, then switched it off again.  The same problem occurred - it took several tries to get it to boot.  The exact sequence goes like this:

1. Switch off at night.
2. Switch on next day.  Screen is blank, no beeps, no access to BIOS.  Hard drive spins up.  CD drive is not accessed, nor is floppy drive.
3. Wait a while to let PC warm up.  May get a few noises between click and beep, but nothing that matches any of the beeps in the beep table.
4. Switch off and try again.  The PC may start up.  Sometimes the CD drive is accessed around now but the boot procedure doesn't get any further.
5. If the PC doesn't boot, repeat steps 3 and 4 until it does.

This problem is one I really need solved.  Help!!!

[Computer_Commando]

...For some time my PC was on 24/7...

Open it up.  Probably full of dust.

[gussery]

Just for fun make sure your monitor is off when you turn the computer on, then turn the monitor on after a bit.

I have seen monitors try to pull too much power and the computer starves for the same power.  I don't see this much anymore unless they are older monitors and computers.