Ask your friend what happened the last time he drove it that might give an indication as to what the problem is. If you think the engine might be seized, disconnect the battery, remove the wire harness from the ICM, and use a wrench on the crankshaft pulley bolt to try to turn the engine over. If it won't turn over remove all the spark plugs and try to turn it over again.
Your friend'* description of the symptoms does not make sense. If the engine is locked up (seized) it won't crank (turn over). If it cranks, it'* not locked up. On the other hand, if the motor is seized trying to start it could cause a lot more damage. that is why I suggest you try turning it over by hand.
What tools do you have access to, and what level of mechanical knowledge do you have for working on cars?
2001 Bonneville SSEi (retired at 365,000 Kms.)
2014 Jeep Grand Cherokee Overland (yes, I know its not a GM)