Hi Annabel,
Welcome to the community!
You can indeed claim back the VAT on the computer you purchased. You can claim back any goods as far back as 4 years that are business related and providing you still own them (for services this is 6 months).
I would advise that you put an expense into QuickBooks and attach the receipt/invoice if you still have a copy against this expense. Date this for the first day you started trading as a sole trader.
Do you currently have an accountant/bookkeeper to help you along the way?
Kind Regards,
Emily Mockett
