Vostro 3250 SFF totally dead, PSU seems OK, power switch does nothing

Just over a year old but basically untouched PC, been stored properly, do dampness or vibration.

Plugging in power supply makes the usual fizz sound so is getting power OK and the PSU test button lights green and powers the fans, but nothing else does, DVD drive and hard drive doesn't open/spin but not sure if they should.

I am guessing the fans are powered directly off the 12v and main power connectors, so power is obviously getting to the board at a basic level. As I said pressing the power button does absolutely nothing. Unplugged everything from the PSU it starts up OK and the light is green. Did the same with only the board in, even removed wifi mPCIe, RAM, drives. Nothing, not even a beep.

The PC is too decent to throw away and I want to get it working. I don't like the power switch, this could be faulty I guess, I disconnected it and tried another 2-wire switch on various pins on the connector to try to get it to fire up, nothing. Where can I get hold of another power switch, motherboard and PSU in the UK? I've already tried ebay everything is in the US. I did try the dell website, but it helpfully tells me zero parts are available. 

Thanks