S-10 trying, but failing, to start

I have a 1999 Chev. S10 w/ the 2.2 4cyl that has yet to give me any huge problems, even after 206,000 miles. It started and ran fine as recently as one week ago today when we returned from a long trip. Upon trying to start it today, I found that the serpentine belt and associated wheels start to turn (for maybe a second) but then stop. There is a continuing hum (louder than the fuel pump) until I release the key. There also seems to be a slight jolt from both the engine and directly under the cab as the engine stops cranking even though I tried to start it both in and out of gear.
To reiterate, the truck started fine, sat for a week, and now won't start. It does not appear to be a starter or a power problem as I have experienced both in previous cars, but then again, I am not the expert.