Issue using Kubuntu in Windows 7

I have been facing problems in using kubuntu as I am new user of it. I was using ubuntu before and it was a nice experience but then I wanted to use kubuntu and formatted ubuntu to install kubuntu. I am using windows 7 at the moment. I have a problem that whenever I reboot, it just freezes on log off screen for a long time. After that I am forced to switch it off and restart it. But whenever I do it and go to kubuntu partition, it only shows me a flat screen full of dots. I even tried so many alternative ways to resolve the problem like reinstalling it in windows 7, uninstalling it from control panel but I was failed in doing so because it again give me certain errors. I really need your suggestions to resolve the issue. Please help me out, I would be grateful.
