This may suddenly happen due to any invisible cause. Sometimes your computer starts to load the window but sometimes it stops responding during the start-up process. This problem may be caused due to various factors.
Your system/computer may start loading windows from any external device. First, you will have to check, and remove such kind devices like CD’s, DVD’s, USB Flash drive, and Memory cards. Try to restart your machine. Despite this it fails to start, that means, something else is causing the problem. If your desktop displays error during the start up, means this is probably caused by hardware configuration. CPU, Hard disk, RAM, or graphic may develop an issue.