How long was the vacuum sitting and not used?
Check if the blue LED is lit on the charging base.
If the LED is lit, check for voltage at the charging base connectors. 20VDC
If all that checks out, the vacuum might need to be rebooted. To do that, remove the main brush, then remove the 4 screws holding the battery cover on. Then carefully lift the battery out and disconnect it. Wait a minute, reassemble and keep your fingers crossed.