1997 Ford Taurus steering problems

Something happened to the steering while I was driving a ford taurus rental car that made me lose control and tumble over an embankment. Before the accident, I noticed irregular steering that resembled sterring consistant with a low tire. However, after stopping to check the tires, I found that all appeared to be properly inflated. Approximately 5-10 minutes later, the steering failed causing me to lose control in a curve and tumble over an embankment several times landing on my roof.

I purchased my 1997 ford taurus in february 2010, and shortly after experienced my odometer stopping and my power steering stopping at the same time. It usually happens if I drive the car longer than 30 minutes, or if I sit at a stop light to long. It also seems to happen at speeds of 40 MPH or higher. I also noticed that my transmission will slip, and I will find my car moving forward after stopping. I have gotten used to staying a good distance from cars so I have room to stop.