Forum rules
There are no such things as "stupid" questions. However if you think your question is a bit stupid, then this is the right place for you to post it. Please stick to easy to-the-point questions that you feel people can answer fast. For long and complicated questions prefer the other forums within the support section.
Before you post please read how to get help
Hold Shift right after powering up your pc. The Grub menu will appear. Use the keyboard to select booting with the previously working kernel. After logging in, Update Manager - View - Linux kernels - select the one that wasn't working for you, Remove.