Since a "screenshot" is a dump of raw video memory (to a file), the fact that the screenshot shows the corruption suggests a possible driver
problem. You should check what driver you're currently using, and if necessary update it to the latest available version for your computer's video card.
Otherwise, if this was some sort of hardware or electrical interference issue, the screenshot would likely look perfect - the corruption would only be visible on the screen(s).
It has nothing to do with the fact that you used to run 32-bit Vista. 32-bit and 64-bit drivers
are completely different. It is literally impossible for a 32-bit video driver to be accidentally used with 64-bit Windows.