If you give complete and detailed information about your setup and the issue at hand, such as your platform (Mac or Win), exact versions of your OS, of Photoshop and of Bridge, machine specs, what troubleshooting steps you have taken so far, what error message(s) you receive, if having issues opening raw files also the exact camera make and model that generated them, etc., someone may be able to help you.
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It's a computer at school so I just know it's Photoshop CS5 on Windows 8. The tool was acting like that when I first open Photoshop and I didn't do anything else. No error message.
Maybe someone at school created a preset for that tool -- open the Presets panel.
If no presets, what settings are you using -- size, hardness, spacing, angle, etc...?
try increasing the size of the selection tool.using the right bracket on the keyboard or on the tool menu.
this happens to me when the selection tool is very small.