I have this exact same problem. I recently had computer screen problems and assumed it was related, but seems not. I am also having trouble controlling font sizes in Internet Explorer, and colours in Windows Media Player. I am running an early version of XP. Excel is 2002. Any advice much appreciated.
I formatted a spreadsheet with fill colors and font colors in various places. I then entered my data. I saved and closed. The next day when I opened the spreadsheet it appeared to have no fill color or text color. I thought I had possibly not saved so I clicked on a cell to reformat it and found that it had the appearance of a cell with formatting. I then went to print preview and sure enough the colors were all in their proper places. It even printed out correctly. After closing print preview I attempted to change the color of the fill. It seems to be locked somehow. I can change data but not the format. I even tried to copy the sheet to a new sheet but it simply copied it with the same appearance of no colors. I haven't a clue what's going on here. Has anyone had this happen? What is the fix... other than rebuilding that sheet from scratch.