The Program Files directory is protected so you can't mess with it, so you will get a prompt asking for a password to grant access. That's how it works.
HOW are you trying to install apps?
Actually, most cases where folks report such problems is when they are using a PC that has been configured to DENY admin access, as is typically the case with a Work computer (i.e., one provided by your employer). Is this the case with your PC?