See if https://www.google.com/search?q=ransomware+.gero+decrypt leads to a decryption tool or method. Or maybe just pay as asked.
And, of course, clean your PC or go back to factory conditions.
And, just a tip, in the future be careful what you install, especially if it comes "from the internet". The internet is full of threads.
If no luck with decrypting, you only lose what you didn't backup. That should be only unimportant files, since one should backup important ones.
A few days ago I tried to install some software from the internet, during the installation process I saw some unusual activities on my computer (scanning all my computer files). During this time I tried to stop or cancel this installation process but I can't, so I just switch off my computer and restart again then I see that all files in my drive are not opening and their extension is changed to .gero.
After that, I google for .gero extension. After that, I came to know that I have a ransomware attack on my computer, then I try to decrypt with STOPDecrypter software, But it can't help me. So please help me on this how to bring some important files which are encrypted with .gero virus.