Aftermarket HU

Wondering if anyone can help?

Got an issue with my 06 Octavia. Had a Pioneer deh-3400ub lying around that I used in my old car, tried to put it in my car & it won't power up. The original HU works perfect, no issues. Tried a Sony aswell, when plugged in you can hear a noise as if a cd was coming out but still not powering up properly. Went to Halford's for leads and whatever else I'd need, the guy ended up coming out to the car & said I need to book an appointment with him to get it tested with a multimeter, not really keen on doing this! 

I had a Sony in it before too, a different one to the one mentioned and it also worked fine, just had problems with the k-line wire. I would've put it back in but I've lost the stereo lol 

Anyone know what could be wrong? I'm stumped!