[Leems]

You've got a loose connection somewhere. First, try the negative and positive battery terminals - remove and secure them. BTW: what is the battery voltage with the engine shut down and also at low idle?

Next, you could lift the head unit out and check those connections (easy to do, check YouTube).

Have you had any work done on the vehicle prior to this anomaly?

 

[Leems]

U120300

I didn't look it up - what fault code is that?

Since you having more than a single issue - in fact it seems like several, almost unrelated - the chances that you have one primary problem seems pretty high. I'd look for either a loose connection or a corroded connection everywhere mainly around the engine compartment fuse box. You could use an ohmmeter and look at every visible connection to chassis ground, for example.

Don't give up on the vehicle, there's likely a fix for what ails it. Good luck.