1997 Ford Probe Won't restart after jumping

"What next" depends on what's wrong, and we have no way of knowing that. You could simply have a bad battery, but the charging system is suspect too. The first step is to charge the battery at a slow rate for an hour, then measure its voltage. If it's good, it will read close to 12.6 volts. If you find it's around 11 volts, it has a shorted cell and must be replaced.

If the generator is not recharging the battery while you're driving, the battery may be run down. It can take an hour or more to fully charge it, and it can take ten to fifteen minutes for a totally dead battery to START taking a charge. That means that while jumping it from another car might get the engine started, the battery won't last long before the engine stalls.

With the engine running, measure battery voltage again. It must be between 13.75 and 14.75 volts. If it is low, a full charging system test is needed. That requires a professional load tester.