Good Morning!

You do not mention whether you have a manual transmission or an automatic transmission in your Geo...

If it is a manual transmission, you probably have a failed clutch. The car is going on 14 years old; if it is the original clutch in the car it is well past it's life expectancy. The transmission has to be removed to replace a clutch, and the job typically costs in the neighborhood of $500 or so.

If it is an automatic trsnsmission model, then you should check the transmission fluid level, and fill it if it is low due to a leak somewhere. A low fluid level will result in transmission slippage, making the car not move. If the fluid level is full, then there is an inttransmission failure that will need to be diagnosed by a transmission mechanic. Transmission repairs vary greatly in cost, depending on what the failure is. Diagnosis is usually inexpensive since it does not take much time (usually under an hour).

I hope this is helpful to you; if so, an accept would be most appreciated! Thanks!