Can't login to Debian after installing driver

Dear NVIDIA Support Team,
I have recently installed the latest driver for the GT210 card found on your website on a desktop machine running Debian 10 with KDE Plasma. According to the instructions I’ve added your repository to the sources list of apt, ran the update and installed the driver, then rebooted after the installation, as it was suggested by the guide. Unfortunately after the restart the login screen was not displayed, only a small underscore mark in the corner (not blinking) and a mouse cursor. When opening the console, I was prompted for login, but when typing in either the username, or “root” I wasn’t asked for a password, but received the error message “Incorrect login”. The issue remained even after removing the graphics card and using the integrated VGA port of the motherboard, or when trying to start the system in recovery mode. This way I’m not even able to log in just to purge the driver and continue using the one shipped with Debian 10. Please let me know how I can fix this issue. Thank you in advance for your help!
Best regards,
Tibor Gacs
PS: one more thing, the whole machine was installed with LVM