To add to Kyles post, I had a similar issue. The HD 4xxx series are no longer supported, and when loading Win 10, I noticed the default Windows driver. I right clicked on this and 'update driver' and did the trick. It recognised it. I have two pc's which have HD4300 and HD4550. I had to do this on both.
After this, I tried to download the Catalyst Control Centre, but won't download due to the age of my graphics card which alough managed (in the end) to get 1920x1080, there was a black border around. HOwever, there is a work-around for this in Regedit, but to be fair isn't a Windows / Microsoft issue as it's down to AMD/ATI as the drivers are no longer supported.