I will need a little more information.
2.How old is the computer?
4.Have you recently loaded any software or installed any new hardware?
5.Do you have a USB Hub attached to the computer or ANY devices for that matter when you turn the computer on?
6.Are we talking about a desktop computer or a laptop?
A blue screen appearing on the computer is known as a Windows crash. This means that something is not correct in the operating system. However this can be caused by operating system damage, viruses, driver malfunction, incorrect drivers, incompatible software programs, damaged registry (These are all known as software issues). This can also be caused by Bad Memory, Bad Hard drive, CPU issues or mainboard problems (These are all known as hardware issues).
Before I can tell you what your issue is, I will need a little more information such as there is a code at the bottom of that blue screen. I need that code number.