Hello Ikatz and welcome to PC-Guide.
You could use a copy of my Diagnostic Flowcharts.
Send me a personal message requesting them [zipped or unzipped] and giving an e-mail address to send them to.
Here’s one possible route through them:
START UP TEST
1. Is the PC dead? No. [You have fans & lights]
2. Did POST appear to run? No.
3. Were there any audible beeps? No. [a single beep indicates successful completion of POST]
4. The Power-On Self-Test failed to complete. [NO POST]
1. Are the PSU voltages correct? Check them if you can. If they are not you may have a faulty PSU. Assuming they ARE ok then:
2. Disconnect all peripherals and system adaptor cards except the keyboard and video card/monitor.
3. Does the POST now run? If it doesn’t then your system board [or something on it (video card, CPU, memory)] is faulty. If it does run then:
4. Re-connect the floppy disk drive and run advanced diagnostic software from a floppy disk.
[Get “TuffTest-Lite” from http://www.tufftest.com/free.htm or better if you can. This is simple and basic.]
5. Does the system board pass? If not then it is faulty. If it does pass then:
6. Switch of and re-connect ONE peripheral/adaptor card.
7. Does POST now run? If it doesn’t this last device connected is faulty and should be disconnected. If it does run the device should be tested using the diagnostics and if it fails is faulty and should be disconnected. If it passes it's ok and should be included.
8. Repeat from step 6 until all devices are tested, all faulty are excluded and all working are included, then re-test the system.
If you want to reduce the level of difficulty for the first attempt at a fix, assume that the PSU is ok and leave out the tests with diagnostic software.