My '97 volvo S90 does run, but had a misfire issue which I wanted to have the mechanic diagnose.
I called a tow truck to tow it to the mechanic for me. When the tow truck got there, it turns out the volvo battery was low and needed jumping.
I connected one end of the jump cable to the volvo battery while the tow truck driver connected the other end to the boost car. He made a mistake and connected the cables in reverse (neg to pos and pos to neg). The error resulted in spark at the booster battery and he immediately corrected it.

I got in and insert key in the volvo, but no sound from the starter. Then I noticed that there was no red or orange lights on the dash either. No headlight and no horn. I told him that I think he blew a fuse when he swapped the jump cables but he insisted that Volvos are funny like that and he has had some that sometimes won't start due to the alarm. Bottomline is that I used to jump this car and it will start, but since he swapped the battery cable by mistake, thats when all this no power across dash and starter started.

Facts to consider:
1) fuel pump relay does click and pump does buzz/prime when key is turned.
2) Alarm does sound when battery is reconnected and driver door is opened without first locking and unlocking it (horn blowing).
3) Turn signals does flash once when battery removed and reconnected.
4) Locking and unlocking all doors still work fine using key in driver's door.
5) No horn, no dash lights, no starter action.
6) Parking lights work when light switch is turned once. Turn twice and it goes off and no headlights come on.

I did some research online and the best I found was to use key in driver's door to lock and unlock 5 times. I did that yesterday and the condition remained the same.

Does anyone know if this is a fuse or relay problem and how to go about troubleshooting it? Personally, I think it has to do with crossing the battery cable. Everything worked fine until that incident happened. I looked at the fuses and they seemed alright.