Email the web page address of this dialogue to yourself. Go to all the individual web pages I've given you links to and email those to yourself so you have access to them if this page is unavailable for any reason.
Assuming you were issued with a 2014 tax return after 5 April 2014 which you should have been given that you registered as self-employed, you will have your 10 digit UTR (Universal Tax Reference). Call HMRC on the number here
and given them your new address as soon as possible.
Your activation code expires after 28 days so if you registered about a month ago I'd give it a week for your new address to filter through the HMRC computer system and then do the following:
1 Read the notes here
2 Assuming that the 28 day activation period has passed and if I were you I would assume that as this process is easier, go here
. Login with your user ID and password ***** select the service you wish to have cases to. You will then be issued with a new activation code.
3 When you get your activation code, it will give you instructions as to how to use it.
4 Once you have activated the self-assessment online service, take a look at the tax return demonstrator here
. The complete registration process is demonstrated here
if you need to refer back to it. There is more helpful information here
As you came from abroad, your first tax year in the UK will be split between pre-arrival and post arrival in the UK. if you need to complete the residence, remittance pages SA109 here
and the foreign income pages SA106 here
you will not be able to complete your tax return online as the HMRC software does not cater for such cases. Refer to RDR1 here
and, in particular, section 9 to determoine whether you are affected by these rules.
I hope this helps but let me know if you have any further questions.