I assume, you are running at least Windows 2000 or XP.
I that case, it is rather simple:
Set up “good” passwords for all the user accounts and use the NTFS file system.
It is btw very recommended to use a restricted acccount for daily work, and administrative accounts only for system maintenance. In case you are using XP Home, start in safe mode and set a password for the user “Administrator” which is hidden normally. This will prevent any user from accessing your computer. Even safe mode won’t help there.
In order to prevent booting from a floppy or CD disable these boot options in BIOS setup. Also set a Password in your BIOS. For further details, refer to the manual of your mainboard.
Is there a way to put a password on such functions so that the ability to use them is more limited?
Of course, there is