I recently encountered the below error while uninstallting SQL Server 2008 Express tools, because the insallation got failed and not moving forward.
SQL Server Setup has encountered the following error:
No feature were uninstalled during the setup execution. The requested features may not be installed. Please review the summary.txt logs for further details.
Error code 0x84B30002.
Follow the below steps it may help to uninstall, Before follow this procedure please make sure you have some idea about registry
1. Open Registry Editor
2. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\
3. Browse Ids one by one and identify the GUIDs for SQL Server 2008
4. Run the below command for all SQL Server 2008 Guids one by one
From command prompt
msiexec /x "Guid"
Remove all Guids which are releated to SQL Server 2008 R2 / Express
Restart the system and verify in the control panel - program and features
Then you can proceed with a fresh copy of installation.