Hi welcome to JA, my name is ***** ***** I will assist you with your query today.
The most likely fault is the power supply, can you confirm if the power supply was the one shipped with the keyboard (PA-5D)?If you have a multi meter, plug in the power supply and use the probes to check your getting 12V across the centre and outer part of the round plug, if you dont you could look for another product which takes a 12V input and try the power supply on that to see if it powers on. Failing that go down to your store and buy 6 "D size batteries" and put them in the keyboard. If the keyboard comes on then its the power supply if it doesnt its looking likely to be the keyboard, at which point it would probably be uneconomical to repair.
If it points towards the power supply you can buy a replacement for under £12 here.
Please let me know how you get on testing the power supply.