Adobe Acrobat printing issue

I have Adobe Acrobat 8, Windows 7 Home Premium, HP Photosmart 6520 All-in-One (just replaced my old 2610).

Quite recently, on the old printer as well as the new, when I have attempted to print a pdf file it has printed as solid black or like a negative (solid black background with text areas "highlighted" in white).

What's going on and how do I fix it? This must be an Adobe issue, as both printers print other documents correctly, regardless of source. This just started (before I replaced the 2610 with the 6520) so I know it's not a printer issue; I've previously had no problems whatsoever printing pdf files of any kind.

(Tried to get into Adobe communities, but the system is a nightmare and I can't even sign in and get a question on!)

Thank you.