How to set password to prevent sleeping or shutting down computer

You can setup group policies which only allow certain accounts to do what you want.

http://www.addictivetips.com/windows-tips/how-to-disabl...

Make sure you know what you are doing with this, you can lock down the computer so well even the administrator account can't do anything.

what happened when they hit the power button?

i just dont want people to shut down my computer when im not sitting in front of it

you cant. the power button overrides all passwords.
yes you can stop users from shutting the system down/sleep via windows by setting up a user account. but really what you want to do cant be done because you cant disable the power off button.

There is actually an option to do that. It's a rarely used option but it is indeed possible  



Take a look HERE in regards to how to change what the power button reacts when it's pressed. There is also a secondary thread in that link that will guide you through removing the hibernate and stand-by buttons entirely.

IMPORTANT NOTE: Local group policy is only available in Windows 7 versions Professional and above. This option does not exist for Starter or Home Premium.

I think the first step here is why you need to worry about this in the first place. If you have roommates, just tell them not to shut down the computer.