Are there any other websites on which hyperlinks are invisible? If so, I’d guess that somewhere you have a setting which is displaying hyperlinks as white text on a white background.
Do you have a flat-screen/LCD monitor? Sometimes things can appear invisible on those from certain viewing angles.
Have you got any kind of adbuster software running on your computer? ISTR someone starting a thread about having to disable his program in order to read the board.
wanders off to do a search
Here we go, it was a program called webwasher. Looks like it did more than just screen out the thread links, but this might be a similar problem.
Someone else just asked about a similar problem.
The cause may be your color scheme.
In the browser options, there’s a choice to use the main windows color scheme. Some “Theme” screen savers mess with those and can make certain colors so close together you can’t tell them apart.
Or, someone/someprogram may have set your colors to “Accessibility Hi-Contrast”, which uses only a few colors, and many colors “map” into the same one.