@Palash
Note that the latest version is currently PVA v2.8.7.
You can re-run PVA or click the WhbPack application in the software directoty to update the software to the latest version and try again.
Are you using any proxy in your browser please? Try to remove it, then go back to check if you can login in the software.
Try to turn off your firewall in your computer control panel, then check if you can login in.
If you turn on vpn, turn off vpn and try again.
If it still cannot work, could you please send pictures of the problem you mentioned?