The box under the seat controls the central locking system, immobilizer, and some window functions. They are prone to corrosion from accumulated moisture in the carpet padding. It may be the cause of the window problem, but if connectors are plugged and seated and the car starts and runs the window problem is more likely elsewhere.
Did the windows function normally before you removed the seat? Check fuse B6.
Even if there is nothing wrong, after having the battery disconnected, the windows need to be reset by lowering them all the way, then raising them all the way back up.
For a scan tool, I am currently using the one described in this thread:
https://986forum.com/forums/boxster-general-discussions/86122-recommended-alternative-scan-tool-code-reader-durametric.html