Sometimes this little goofy thing will happen, i have not found out exactly what happens.
The fix that i found to work about 99% of the time is to remove the radio, unplug the wiring harness from the rear of the radio, remove the fuse under the connector. make sure the mini 10amp fuse is not blown and plug it back in, plug the wiring harness back in and push the power button on the radio, it should turn on. If you need the radio code, before pushing the radio back in, write the serial number down (serial number will look like vwz5z........) and post it here i will supply you with your security code.
here are the radio keys you will need to remove the radio:
Please click accept, Feedback is always appreciated!
the keys might come with instructions, but if you look in each corner of the radio you will see 4 slots to stick the keys into, you will want to stick the angled side towards the radio and you will feel them click into place, and simply pull on them. The radio will slide right out.
As, for the connector harness locate the bottom portion of the connector you will notice a little stub sticking out a bit, push down on this piece and it will rotate up and unclip.