How do I repair my Ryobi 26cc Petrol Strimmer?

I purchased a Ryobi petrol strimmer in August 2007 and have only used it 4 times for 20 minute periods. Last month in April while using my stimmer the engine stopped and I can't free the pull cord to start the engine. Iv'e used the correct mix ratio of 2 stroke and unleaded petrol and have sprayed a light amount of WD40 but still can't free the cable as it's jammed tight. Has this strimmer siezed for some reason after being used so little. Any advise appreciated as I have mislaid the user manual and reciept. Disapointed on the short life span in return.