Is this a scam, an identity theft, or phishing?

[ellenrr]

Today my computer suddenly froze. A message appears that Microsoft blocked my computer, that I am infected with a virus and spyware, that my personal info is compromised, and to call this # right away.
So I call the number and -- yes I am stupid - I let the guy take over my computer.
After 30 minutes of showing me how much was wrong with my computer, he tells me for $120.00 they would fix my computer.
I decline, and hang up.

Someone else tells me to unplug and plug in my computer.
I did, and my computer now appears to be acting normally.

So I wonder how much harm I am now open to.
I have changed credit card and bank account.
The company that wanted to sell me the $120.00 service contract is
https://www.sktechserve.com/technical-support/

My computer is a dell desk-top, OS is Microsoft XP.

Does anyone have any suggestions how I can protect myself?
I mean from identity theft.
Is it too late?

Thank you.

ellen