Is is unlikely that turning the computer on, retrieving a CD-ROM and turning it off again was the sole cause of the problem, but it can't help, I'm sure. (Personally, I have "test" machines which get abused like this all the time.)
My first step after ensuring all connections are firmly in place is to take it to your local computer-reseller and have it checked out, which will probably cost about 1 hours labour, and will probably be included in any time the spend actually repairing the machine. (I don't know about practices or labour-rates in the Netherlands, sorry)
I will assume that the power supply doesn't even power up, meaning that it is likely to be one of two things: Power Supply or Motherboard.
A power supply will probably cost about 20-25 Euros to replace (if needed) and a motherboard might be about 75 to 150 euros to replace, plus the labour.
I will also assume the the CPU you have is current (P4/Celeron socket 478 or Athlon K7 socket 462). You may still be able to find motherboards for PIII/Celeron socket 370, but they are getting more rare every week.
I've got a PC [clone--Dynabyte] which has never once caused me a problem...yesterday my step-daughter started it up to retrieve a CD-rom she left in the E; drive but didn't wait for the PC to completely power up..[never even got to the welcome window in XP]..apparently she opened Cd-rom drawer as it was still powering up and then immediately hit the off button and shut down the PC [as it was still turning on]
The bottom line..we tried to power up this morning and nothing happens..totally dead. The PC is receiving current and still shares current to the scanner and the other hardware attached..but the PC itself is dead.
Can anyone tell me what the most likely problem can be..if indeed the shutting down in the middle of starting up could have caused this..and how to go about fixing it..?