Does it still load the Sony Vaio splash screen when you turn it one? First do try to remove the Windows XP disc off the laptop then reboot again. If these doesn't work do try these troubleshooting steps that may help.
- Do a hard reset, remove the battery (if not built in) and AC adapter then press and hold the power button for 20 seconds then see if it will boot up normally.
- Next is to test the AC adapter and see if it's supplying enough voltage to power the laptop or better yet try another AC adapter that has the same voltage.
- If there are lights on the laptop indicating it's on connect an external monitor again and see if you'll get a display.
- Also do try and reseat the RAM, remove them all for couple of seconds then put them back in making sure that they are all seated properly into each slot.
- If all these will not work the problem lies in the motherboard of your laptop.
Thank U very much Laptop_Nerd ! Ihave tried every/any points U suggested to me, but no result... So may be in the motherboard is the problem... I will look for same model second hand and will try to repair it. Thank U again!
PS: Excuse me for the bad English - I teach it continuously...