This might not be relevant as maybe you've already tried this ... but have you looked in your add/remove programs to see if there were remnants of past SQL Server 2005 installation causing conflicts/problems? You can try removing everything there, then use the SQL 2005 installer agian?

Although I have a different version and experienced different behavior I had installation troubles too.

I used Add/Remove programs... removed everything SQL 2012, and then re-installed as if brand-new and was successful.