Loss of Steering control, need help!

Hey all,
I own a '93 SLC and am having some problems relating my steering. Ok, So i'm driving down the road and all of a sudden my steering gets really stiff, the check engine light comes on, battery light flashes and the check oil light goes off as well. I have to fight the car over to the side of the road, trying not to lose control of it. I then turn the car off and then turn it back on and everything is ok.
This has happened 2 times this month and is very sporatic. I'm thinking that maybe something is wrong with the powersteering, but im not too sure. The funny thing is that i had the car checked out just last week and the shop that i brought it to said that all was ok. Then I get in my car today, and the problem happens again. If anyone here has any idea of what this could be please help me. This is turning into a HUGE saftey issue and it's to the point where i absoloutely do not want to drive my car in fear that something major will happen.
The problem occurs at the most random time and nothing that is in a chain. The first time that it happened was when i was taking a left hand turn at about 25mph, the car just wouldn't turn, straightened out and i couldn't move the steering wheel to the left at all, only straight and a little to the right.
The second time it happened (today, about 3 weeks from the first time) it did it when i was doing about 50 on a straight away.
The car doesn't shut of, and all of my electronics are working fine, nothing is shutting off. The check engine light flares up, check oil light, and the check battery light...
please if anyone could help on this one i would greatly appreciate it!! Thanks in advance!!!