How can I prevent someone else from using my PC?

If you are using Windows XP, you can password protect your user accounts. You can access your User Account settings from the Control Panel. There is a User Accounts icon. You shouldn't have any trouble figuring out how to set a password once you are in there.

Turn it off and lock it in the closet. Physical security is the only security. It is trivial to break into any xp machine if you have access to the physical box. Otherwise, do what mharleman said. Put a password on all user accounts on the box. If you're using XP home, upgrade to professional.

If you have physical access to a machine it can be broken into without too much difficulty regardless of whether passwords have been set on user accounts.

As has been stated above you will need to resort to locking the machine away to prevent unauthorised access.

Steve

Look for your motherboard manual. Check how to enter your bios. It depends upon the computer some use DEL, an Fx key where x is a number. You can specify a password before the computer even completes its boot up.

Scouter's recommendation is a good one, but can still be bypassed by someone if they have enough time alone with the machine. If you're still concerned about access a layered defence is best e.g. don't rely on one mechanism, ues them all - set user level passwords, a BIOS password, and lock the device away when not in use.

Scouter and rattyvulcan are right. What it boils down to is that you basically have to define a certain level of risk as acceptable. Ultimately, if I have physical access to the machine, with enough time and effort I can harvest everything. Gauge potential users' abilities against your own tolerance for security measures. For example, if I want to block my roommate from accessing the machine, I would probably set a BIOS password as well as a windows password. Unless my roommate is a hacker, and then I would probably go for a new roommate. Ha ha. There are also USB dongles you can get that will "lock" your computer. Or, you can change your paradigm and instead of stopping someone from using the computer, stop them from getting your data. In that case encryption is your best bet. PGP is good, or Windows XP has built in encryption mechanisms, but be sure you understand how they work before employing them. A skilled hacker could still potentially get at the information.

Any other suggestions, or should we drop it until ralonzo7 replies?

- Slog