Has my computer been hacked?!

My problem -

The other night I was typing an email and a strange box came up on screen (like a pop-up except it was black), flickered a few times and then disappeared.

This made me nervous and when I went to check my Norton Anti-Virus/Security both icons were no longer present in the tray at the bottom of the screen.

I opened Norton Security from another place and everything had been disabled... firewall, anti-virus, auto-protect... everything.

When I tried to click on anything to change the settings I was told I don't have access to perform these task... didn't have supervisor status or something.

I also have running the Windows XP security center w/Firewall & antivirus. When I checked the windows security center, Windows antivirus had ALSO been disabled. The Windows firewall was still enabled BUT "remote assistance" had been checked on the exceptions tab!!

I was somehow able to run the norton virsus scan and nothing was detected. I shutdown, rebooted and everything appeared normal again. Norton was fully enabled as well as Windows antivirus. I ran a live update with Norton and did another virus scan and still nothing was detected.

This is very scary to me. Has my computer been compromised beyond repair?? Does anyone know what this could be? Was this a hacker? A trojan? What steps should I be taking?

ANY help is appreciated...

Thanks in advance!