Vista Defender won't open after CCleaner installed
I think we need a bit more info here.
Which version of ccleaner have you used and did you download it from the Piriform site?
Did you do a clean with just the default things ticked or did you tick some extra things?
Did you do a registry clean? If yes, did you make a backup when offered the chance to do so?
Also I hope you are talking about Windows Defender because Vista Defender is a rogue program.
Google result suggest Vista Defender is FAKE and needs removing. e.g.
http://www.myantispyware.com/2010/03/18/how-to-remove-vista-defender-pro-removal-guide/
I installed the 3.15 version from Piriform on my Dell laptop using the MS OS Vista system, and upgraded it to 3.16 recently. I followed their instructions and backed up the registry when asked. However, I am now unabled to open up my MS Defender and have to run a MS Essentials virus scan every 10 to 15 minutes. My computer does run more quickly now but, all that is lost when I have to take time to run the virus scan.
When Microsoft Security Essentials is installed it automatically turns Windows Defender off.
Ccleaner has nothing to do with it.
However if you have MSE ticked in ccleaner applications list (it is usually listed as something like microsoft antimalware) it will prompt MSE to tell you that you have never done a scan, so you could untick to avoid that that happening.