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That's a shame. It's something that might be corrected, though.
1. a watch-size battery is sometimes defective. ?Try another battery?
2. did any part fall out when you took out the old battery? some watches regrettably do have a little jigger of metal inside with the battery, that can fall out, rendering the watch inoperative when it is not put back in correctly. I had a case like that once.
3. if the watch is not new, it may be reluctant to re-start after stopping. (Not that a watch with an LED display is likely to have this problem.) Leave it on a shelf for a few days, take it and give it a tap, it might possibly come to life again.
After which, it will have to be taken to a watchmaker's shop to be opened, examined, cleaned perhaps, and hopefully restored to operating condition.
Note: if the battery you replaced the old battery with was not an exact replacement, that could be a problem too.