I upgraded my Windows 7 running on Dell Vostro 3550 today using the Microsoft Windows 8 upgrade and everything was smooth until when Windows 8 was getting my devices ready. The installation process ran till 79% of preparing the devices and then ran into a black screen. Although, I created repair disks prior to upgrading(as all of us do), but I think this is worth to mention that one of the beauty of Windows 8 upgrade is if the installation fails for any reason, it automatically switches back to the last running OS where we started the upgrade from.
Hence, I rebooted my laptop from the black screen and it told me that the install was unsuccessful and took me back to the Windows 7 screen where I started from. I thought it may be my mistake at the first shot, and thought of giving it a retry. I retried the upgrade and noticed that the black screen problem occurred exactly at the same place (79% updating). This proved me wrong and made me feel there is something wrong with any of the drivers. I double checked my drivers and noticed that all of them are compatible with Windows 8. Going through Dell Support, I came across this link and found that I had to update the BIOS before upgrading to Windows 8. If you are using any other Dell laptop ,you can check with the same link if you need to do this exercise for your specific model. This was the key. I downloaded the BIOS update for my Vostro 3550 from here and installed it on my Laptop before going for the upgrade.
The upgrade took around 30 minutes and everything worked like a charm.
Hope this post can help other users facing same problem. Cheers!