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First thing to check is has googlebot has found you. Check your logs if possible to check that. If Yahoo has its likely that Google has too.
or easier to do, use Google to search for site:example.co.uk (with your site name instead of example) to check that Google is aware of your pages.
Next look at the physical location of your hardware is it physically based in your target area. Does it have the right county code code too, say www.example.co.uk for example for the uk. Sorry if thats obvious but your question was wide open.
Next how old is the site there may be a delay in google ranking new'ish sites. Try a search on 'google sandbox' for more on that.
Other possibilities are sharing tcp/ip address with bad neighbours, robot files telling google to go way, having duplicate content being banned/penalised for some reason.
Good Luck.
curiously waiting for your reply