The first thing you should do is check your internet connection. Having an Internet connection is essential for all kinds of online tasks. So make sure that your PC is connected to the internet. Additionally, keep in mind that your browser may have an issue blocking the proper functioning of your Gmail. After a while, you should also try deleting your browser extensions. If this doesn't work, you can always try logging out and logging into your account. If all of that doesn't work, you should send two email messages to yourself.