Problem Statement:
I just tried to reinstall MySQL 5.5x on Windows 7. But it fails at the point where it tries to start MySQL Service i.e ‘start service’ step.

Solution:
1. Uninstall MySQL. (Control Panel > Add Remove Programs)
2. Remove any MySQL Service if existing (: sc delete MySQL).
3. This is the most important step(who would have imagined!) – and the one that causes reinstall failure:
On Windows7 delete this hidden dir: c:\programdata\MySQL
This dir contains some log files etc – which causes the reinstall to fail. On Windows Vista/XP etc.. there would be a equivalent dir too (perhaps in another location).

Note: If readers know where the equivalent dir for Windows Vista/XP are – please let me know – i shall update this post.