After uninstalling with the uninstall option, just delete all the SQl folders from the drives & then go to the registry -->HKEY_Localmachine & delete any entries related to SQL server in the Microsoft folder. Also grant full permission to the microsoft folder in registry before you reinstall.
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**"There is only one difference between dream and aim. Dream requires Soundless sleep to see…Where as Aim Requires Sleepless Efforts to Achieve":-) **