2005 Chevy Malibu; 4-cylinder; Front Wheel Drive; Automatic; 83000 miles

The car will crank, but won't start every time, and sometimes when it does-- in the middle of driving-- it stops and the steering wheel and breaks lock up: the car looses power.

At first, the anti-theft light came on, so we thought it was the key switch. We replace the key switch cylinder and this didn't fix the problem, but the light does not come on anymore.

We then thought it might be the fuel pump relay. We replaced that AND the fuel filter, and that didn't work.

Also, a local dealer said there was low voltage making it to the fuel pump: 10 volts, not 12. They think it may be the key-switch ignition module now?

What could be the problem and what should we get and have repaired to fix it?