Typically this is not a ProSeries issue, it is your computer issue.

Clear the Internet broswer cache. Restart the computer, restart ProSeries. If it still happens go to Task Manager and End Task for any ProSeries item listed. Restart rhe computer, restart ProSeries. It should work.  If not, look into possible compatiability issues with any anti-virus, malware, firewall and other softwares that might be blocking or slowing down ProSeries start.