Is your login issue explicitly caused by captcha? Unpublish CB AntiSpam in CB > Plugin Management and confirm if you can now log in.
I do not recommend using question based captcha for logins. In fact I do not recommend using captcha at all for logins as it's a significant annoyance for users with no benefits and is why it's default disabled. You can disable login captcha in CB AntiSpam > Parameters > Captcha > Legacy. Recommend only using captcha for registrations which you can do with the captcha field in CB > Field Management.