Try running the computer in "Safe Mode" and see if you still get this same WiFi connection problem. If not, then something (software wise) is causing the issue and you will need to figure out what it is.
If it still happens, even in "Safe Mode", then next I would try restarting the modem/router, clear out the WiFi info on the computer and then, once the modem/router is up and running fulling again, restart the WiFi on the computer and try to connect.