The opening and welcome screens are displayed in Windows lowest supported resolution – in all likelihood 640×480 – so that no matter what the capabilities of monitor connected, those screens can be seen.
As you’ve seen, sometimes it’s not always shown well. But this is most commonly a monitor issue, that should be easy to adjust.
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Many, though not all, CRT monitors, have height, width and position adjustments. These allow you to adjust the height and width of the image displayed on the screen, as well as its position on the screen. Ideally you can make the image as high and as wide as possible, while making sure it’s centered as well.
What most people aren’t aware of is that this adjustment is frequently a per-resolution adjustment.
What that means is that if you adjust and tweak your monitor so that it displays your 1024×768 resolution output properly, that may only affect that resolution. If you switch to another resolution, such as 640×480, 800×600 or others, it’s quite possible that the height, width and position will be wrong. Sounds like that’s what you’re seeing.
The solution is simple: with the computer set to display at that other resolution, simply adjust your monitor again. You’ll need to repeat that for each resolution you expect to display.
Now, the initial 640×480 may not be on long enough for you to make your adjustments before Windows completes loading and switches to your higher, final resolution. In that case you’ll need to temporarily switch Windows to display at 640×480, make your adjustments, and then return Windows to your normal resolution.