K5 Blazer

My 2000 Chevy Blazer keeps loosing power, this just started about a month ago after it went in for an oil change. The first time it lost power was at a gas station, went to start it and it wouldn't turn over. We let it sit a couple minutes and tried again, it started fine, but engine light on.

2000 Chevrolet Blazer 2DR ZR2 from North America
"Dollar Store Quality in all regards, YOU'VE BEEN WARNED!!!" What things have gone wrong with the car?