I am running OS X 10.7.1. Whenever my Mac asks for my password, for example to install an app, it fails and does nothing. This is for everything that involves a password on my Mac.
- your user doesn't have administrative privileges
- the username and password combination of the "prompts" is not correct
- you entered the wrong password
Is your user the only account on the Mac and if not does your user have the necessary administrative privileges? Has your password ever worked e.g. for none automatic login?
One possibility is that during the Mac OS X installation a keyboard layout different from your current one was active. So while you thought you set "your" password different characters were actually put in.
If you can't figure out the password e.g. by changing the keyboard layout your only option is to reset it. One method is to boot into Recovery mode:
press and hold cmd ? + R after turning on your Mac
select the Recovery HD for bootup
once in Recovery mode click on Utilities > Terminal
within the Terminal input the command "resetpassword" and follow the instructions
OSXDaily does have another option which doesn't require any restart. Since it's a bug within Lion I can't tell you wether it's still working.
I will use the reset password method thanks!