Hello Mateusz Bedkowski
Were you able to log in to the subscription panel earlier?
Are you getting any error message?
Since you mentioned that login attempted on a second PC was taken (successful), I think the issue is mostly specific to your machine.
Can you try temporarily disabling firewall and antivirus and see if that helps?
Also, can you try accessing the panel from Discovery forum? First, make sure that you have logged in to Discovery forum. Then, on the right side of the forum, there is a dropdown arrow next to your user name. From this dropdown, select "Manage Account". This will open the account page without the need to log in again. Please let me know how it goes.