Trouble booting device

Apologies if this is a duplicate post, but I can't find anyone recently mentioning this problem. I can't boot my device in the normal way, it just gives me a spinning logo and then a blank screen. I can get in by using the boot menu and switching to boot slot B (it says A is locked, which is news to me). Once I switch the slot everything runs normally. When I get in I check the software update and it seems to be trying to install v2.1 over and over again (thought it had successfully completed, but today it seems to be trying to install again). Don't know if this is related to the update but I don't know what else would be different on my headset, which I've owned for a couple of years now.

Any help is appreciated.