Ceist beag gramadach

Yeah it's An tIonad anyway as ionad is masculine and masculine nouns starting on a vowel get a t- prefix.

But I think 'An tIonad Ríomhaireachta' would also be fine in some cases (Focal gives that in one of their examples under 'computer centre'):

http://www.focal.ie/Search.aspx?term=computer+centre


Then again re. An Lárionad Ríomhairí (This is computers in the gen. plural) so if it's a shop selling lots of computers this is a good one to use for sure, would cover repairs etc. too so it catches all.

(Re. An tIonad, I learnt here recently from Múinteoir that you don't need a fleiscín (hypen) after the t prefix if the t prefix is in front of a capital letter as it is clear the noun starts with the capital letter. Compare that to lower case nouns as in 'an t-iasc' where if you'd written 'an tiasc' that would make it seem as if the noun started with 't' so hence you need the fleiscín)