alarm / electrical issues for 1998 Cabrio

My wife and I recently purchased a used 1998 Cabrio.

We have been experiencing strange electrical problems with the car recently, including:
- the "trunk open" light illuminates even though the trunk is securely closed
- the interior lights do not turn on - at all
- the power locks are not working
- the clock re-sets to 12:00 every time the ignition starts

Today I experienced the following: I put the key in the ignition, turned it, and rather than starting up the alarm started blaring. We could not get it to shut off - because the power locks aren't working we couldn't lock and un-lock the doors using the key. Eventually we were able to disable the alarm by disconnecting the car battery. The person traveling with us unplugged each fuse and that didn't quiet the alarm.

The previous weekend we were using a converter to allow us to power our laptop computer with the cigarette lighter, which I think may have caused the minor annoyance problems above. But is the alarm issue related to this or did something else go wrong? What is the likelihood that this may happen again without getting the car checked out soon? Is there anything I can do on my own to troubleshoot or do I just need to suck it up and take it into the shop?

I am NOT mechanically/electrically inclined, which makes me nervous/uncertain about "playing around" with electrical components in the car.

Thank you - Luke