After scheduled timing belt replacement problems.

04 Volvo XC90 app. 108000
This car never had any problems. Took it to the mechanic to do timing belt/water pump (recommended by Volvo after 100K miles). Thermostat housing was replaced as well. Mechanic didn't find anything else. I picked up the car and it was very sluggish. Just within few ft from the mechanic CHECK ENGINE light came up. Went back and after checking the code he said it misfired but it's not unusual. Code reset. Drove maybe anther 10 miles: all control lights lid up, lost power in steering wheel and the engine went dead. Restarted again and it drove fine. Next morning the same thing happened again twice. Towed back to the mechanic. What's happening? He is giving me all sort of possibilities from blaming me for putting bad gas in to just having unexplained issues. I never had any problems with this car. Any help greatly appreciated.