Something could have gone wrong during the upgrade process. It's pretty rare, but it can happen.
The best advice I can provide is to backup an important data to an external hard drive or if you have a hard drive partition like a D: drive, then copy your files there. You are probably going to have to reinstall Windows 8 to get your laptop back into working order. That will erase all data on the C: drive.
Hard Drive Partition - Laptops generally only have one hard drive; the C: drive. A partition is basically a part of that physical hard drive that is turned into a "logical" hard drive; such a D: drive; where you can save data. Thus, you can have a physical 500GB hard drive that is divided into a 200GB partition and 300GB partition. Sometime a laptop is shipped with two partitions. Other times it is not and owners, then create a partition.
To create a partition you can view the following tutorial. If your laptop crashes during the process, it can mess up your data and you will have to do a reinstall of Windows without the ability to backup your data.
https://www.youtube.com/watch?v=FtnsdjoxW0s