I have the same issue with other people for upgrade to Window 7 Ultimate from Home edition. My only concern is that I can not see anything from my monitor if I uninstall ATI CATALYST Install Manager. I have ATI Radeon HD 5450. Is this possible??
By uninstalling Catalyst you are wiping out the drivers or most of them to run the graphics card, hence why you aren't seeing anything. Does your computer have on board graphics? If so, rig your monitor into that while you do the install.
When dealing with the video driver, recommend booting into the Safe mode (F8).
By booting up this way you are using Microsoft's default video driver and not the ATI driver. Since not all computer motherboards come equipped with on-board graphics, this is a more universal solution.
Also, since you won't have the ATI driver in use, it will be easier to install/upgrade it.