I got the following problem handed over to me today: “When right-clicking the sheet itself to do operations on a cell, Excel suddenly fails to show the menu.” Some desperate minutes later (about 40 of them) I found at least a workaround:

Close Excel if it is running. Delete the following key in the registry:

HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Options

Reopen Excel and test if it works now. The Options folder recreates itself with a minimum set of contents, and Excel seems to be working well after this.

You write: 100. Excel writes 1. You write 1. Excel writes 0.01. Sounds familiar? This is because “someone” (not you, of course) went into Tools - Options - Edit and turned on Fixed Decimals.