Tuisku Salminen, start with the more obvious things: "
1. Check the Sleep/Wake and Home buttons. Are they damaged, preventing the device from powering up?
2. Visually inspect iPad for any damage.
3. Check the 30-pin port for debris or corrosion.
4. Check 10W USB power adapter. If you see the “not charging” text next to the battery icon, the 10W USB adapter or connection is not providing enough power to
charge the iPad. Test with a known good 10W USB power adapter.
5. Check USB cable. Remove USB hubs. Plug iPad directly into computer’s USB port. Test with known good cable. Note: The iPad 30-pin USB cable is interchangeable with
the iPod/iPhone 30-pin USB cable.
6. Make sure the iPad has the latest software updates
-- Use iTunes to check for the latest version of the iOS
7. Charge iPad battery
• Connect to a power outlet and charge with known good iPad 10W USB Power Adapter for 10 minutes
8. Reset:
• Press and hold the Sleep/Wake button and the Home button at the same time for at least 10 seconds, until the Apple logo appears.
9. Restore:
• Restore iPad with iTunes. (This restores the iOS)
• Click on Restore in the Summary tab
• If you can’t Restore, go to Recovery Mode
• If you can’t Recover the iPad go to next step
10. Perform Device Firmware Update Restore."
If that does not work, there are plenty of other issues that could cause this. Component failure of the PMIC, shorted filters, failure of the VBus IC, failure of the charging diode, charging coil and or Mosfet. It will all depend on how good your skill of diagnosing and repairing very small components is. You will definitely have to have the tools, and the skills, to solder the SMD components. You also should let us know if this problem just occurred or if anything happened to the iPad. Hope this helps, good luck.