You may have this sorted, but you should be able to change the password easily.

If you go to your profile or your StackExchange network profile, and click 'my logins':
                                    

Then you should be able to change the password:
Note also that the email (removed in the above pic) you may have used as the your username may also show, so you might want to sort something out about that.

Blocking the IP might not be much use unless it is a fixed global IP address for that machine - using the MAC address is a vague possibility, but even then the hard drive could be switched or the MAC address changed or something.

Hope this helps.

You may have this sorted, but you should be able to change the password easily.

If you go to your profile or your StackExchange network profile, and click 'my logins':
                                    

Then you should be able to change the password:
Note also that the email (removed in the above pic) you may have used as the your username may also show, so you might want to sort something out about that.

Blocking the IP might not be much use unless it is a fixed global IP address for that machine - using the MAC address is a vague possibility, but even then the hard drive could be switched or the MAC address changed or something.

Hope this helps.