1. The file is corrupted. Copy it to a USB-stick and try it on another PC to see if that is the case.
2. The folder is inaccessible, so File>Open doesn't work. Then change that or copy the file to an accessible location.
3. Something is wrong with your Powerpoint installation, especially if it can't open any file. Then repair or reinstall.
It's the file, the location or the program. Easy to check. And when you know which one it's easy to solve. In case of #1 you need a backup (if it's your own file) or a new copy (if you got it from somebody else).
When I try to open Power Point 2010 .ppt file I get Error message: There was an error accessing the file. What to do? Help me please to stop it.