Ubuntu won't proceed further than the log on screen

Hello everyone,

I am a new user to the Ubuntu community, and I am facing some problems with the install. I have installed Ubuntu on a virtual machine (virtual box) using an ISO image. After the installation finished, I restarted the VM and logged onto my account. However, after I log on I see the Ubuntu wallpaper for a time (1 minute) and then I get prompted to enter the password again. This process keeps on repeating and repeating. What should I do?