In addition to what Matt said, you need to (legally) show profit to be as low as you can. So you can claim expenses against the income, and those would include the cost of the server and miscellaneous hardware (monitors, cables etc.), maintenance, software and updates, broadband connection, insurance, phone lines. There is a lot you can claim for but need organizing as they are accounted differently depending on whether they are physical assets that depreciate (significant hardware), consumables (e.g. cables, office stationary) ongoing running costs (internet connection)
If there are things in there you are also using privately, not for the business, then you can still claim but a percentage that is the business part. An accountant will get you started off and can advise on all of that. I'd advise at this level go to a high street accountant, not a firm in a big office. Should only be a couple of hundred as Matt says.