The first thing to try that may be helpful would be to try hard rebooting your device.

IPhone - Press and quickly release the volume up button. Press and quickly release the volume down button. Press and hold the side button and when the Apple logo appears, release the side button.

Android - Press and hold your Android device's Power button and the Volume Down key for at least 15 seconds or until the screen turns off. Release the buttons once you see the screen lighting up again.

You can go to Start in the left bottom corner, select the Power button, and then select Restart.

In most cases, it's because you have too many programs running at once or there are too many browser windows open at once. You could have a virus or malware. Or you could just have outdated tech that can't keep up.

First, what you can try doing is check your Recycle Bin to see if the file accidentally ended up there or check you files to see if you saved it in another place. If that doesn't work, you can use the search bar at the bottom right of your screen for Windows 8 or for Windows 10 click on the Start Tab and the search bar should be below the All Programs tab. Search for the file or program there and it should show up, if its on your computer.

If you have a suspicious virus or malware on your computer, you would know because you may see things like, annoying pop-ups, programs crashing, error messages, or you computer is just running really slow.