Hi @Fatma2 and welcome to the community!
It could be that you have been updating over your old system, so it would be healthy for your phone if you backup your important data then factory reset or better perform software repair using Xperia Companion. This will do a clean installation of the latest firmware and will also wipe your internal memory. Follow the steps given in the blue link, do not connect your phone until prompted to press volume down while plugging USB cable
