Screen Flashes for split second - then black sound works

Replaced mini usb charger with part from ifixit Europe - completed installation - but now the screen only flashes on for split second when you press power button or when you open the tablet cover when its supposed to come on. Looks like there is bad connection from battery to screen. Sound works fine. I have checked the digitizer plugs and screen plugs and have taken them out and re inserted them - no change. checked the battery plug as well - fixed the old part and inserted it to see if the part was faulty - still no joy. Amazon - is no help just tell me to buy another one. Have tried the power button 40 second hard reset - no joy - plugged into the PC = charging chime goes off when its switched on but still n o joy. Any ideas ? Could it be the battery ? loath to spend any more money on it