What exact version of Photoshop. What platform, Mac or Win? What exact version of the OS?
No mind readers or clairvoyants here.
Please read this FAQ for advice on how to ask your questions correctly for quicker and better answers:
The mind reader line was unnecessarily condescending, but okay :
Photoshop CS6 64-bit Edition (v13.01.64) fully patched.
Windows 7 (x64) fully patched.
Some ideas to try out:
1. Reset the Type tool in the Options bar by right clicking
on the T on the left and selecting reset tool.
2. Open the Character panel and reset that.
3. Some fonts do not play well with Photoshop such as
Cambria. See if selecting another font helps.
That's it. Others here should know more about this.