Old Mac mini ..messed up time machine

[RAY AGAINST THE MACHINE]

Howdy ! 
The probable answer is to bin it . I purchased a new iMac in nov 2017 (was gonna get another Mac mini but at the time there was talk of Apple scrapping them) . I transferred my stuff from old Mac mini to iMac . I also have an Apple TV box in the living room. Now here's where everything went crazy and annoying : The Mac mini seemed to have inherited a bug from somewhere and has slowed down and not responding to any commands. So I used time machine on my external hard drive. The hard drive is now full. The Mac has gone back many years and even has the old icons from the days of my Bt broadband .

Tbh , the only thing I use the Mac mini for ( or did), was for the iTunes visualiser . I know I can mirror that from my iMac in the spare room but I don't want to keep going back to change the artists I'm listening to. The Mac mini is about 13 years old ( snow leopard is as far as it can go).  So.. have I screwed it up? As for the external hard drive , I'd like to empty it if it is full. My iTunes library has disappeared on the Mac mini, but is still on the iMac . The clock on the Mac mini is years out of date . That doesn't help.  Thanks for reading this weird post 😼

[Booooooom]

Not used a Mac mini and no expert but...

Try resetting the Mac mini PRAM (restart with command, p and r keys pressed - more info https://support.apple.com/en-us/HT204063 Some system settings may be reset doing this.

The above may work on its own but if not/the current issues return, due to the age of the Mac mini the PRAM battery probably needs changing (£30-40?) 

At this stage you should be able to carry on as before but I’d ask myself if trying to use older kit to keep in sync with the modern world is really worth it? Updating the iMac will probably make things worse as you say the Mac mini is at its limit.

maybe time to bite the bullet... good luck

[RAY AGAINST THE MACHINE]

Thanks booom:)

I managed to do the pram thing, when I put the installation disk in to repair . What I'll try and do is erase the external hard drive and dump the Mac mini .