Burned CD or Retail CD? Not enough info. Could have a bad burn - try burning in CLV mode instead of CAV. Copy protection lately even makes my see everything crappy SOny drive not see things first time on retail CD's and DVD's.
Short answer - not enough info on the problem.
ANother idea is that your drives head may be out of alignment. CHeaper probably to buy a new drive than to have it reparied in this case.
-S
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