SC1420 Power light flashes 3 times.

Hi.

I gave my trusty old 1420 a bit of a spring clean today - Doh!  When I try to power up all I get is the power light flashing 3 times then nothing,  no power cycle at all.  I've put myself firmly in the mire here!

I cant find any documentaion about the problem.  I've checked and double checked all the connectors.

Any help very gratefully recieved.

TIA

Jon