First if you are in UK. [it's a world forum]
Go back to the dealer tell them what you've discovered. If they don't want to know and did not get you to accept by signature the faults you may be covered for a refund under the consumer act.
Go to www.consumerdirect.gov.uk click 'contact us' follow through either phone them or email see how you stand.
Unfortunately if a private sale you've been caught.
May not cost much may just be dirt under the keys..
bob
November 2010