A friend of mine brought a GoPro a couple years ago, a hero 3 plus.
Used it a couple times and then it stopped working so he put it in a draw and forgot about it. It’s now mine but it still won’t work.
I brought a new battery and it turned on but was frozen, now it’s completely unresponsive.I’ve tried all the resets I can find on the internet but nothing is working.
I have tried to find a repair place and only come up with two but they seem a bit dodgy.
Any ideas?

Does it work if you take the SD card out?

There is a camera repair place in Horley. I took a fairly new camera in to them,
I bought it very cheap with a lens problem, but the problem quickly got worse.
They told me it would be some amount[60 quid rings a bell] plus a new lens to
repair it. I went back to get it and they had checked with Samsung, it was
under a year old so Samsung footed the bill.
I just looked up camera repairs on google and they were the nearest.

No, it doesn’t. Also tried removing the battery and sd card and plugging it in as it should power up like that….. but it doesn’t
I was thinking I would need to take it to a GoPro specialist? I’ll ask at my local camera shop

Contact GoPro with the serial via there web page. There were a few issues with those cameras that resulted in the being bricked. I had one replaced. Its a software rather than hardware issue.