Whole Appearance Of The Display Is Rather Unusual

Problem is with an Acer 5103 laptop running Vista Home Premium. After several months of fairly satisfactory operation apart from the normal unexpected shutdowns there is now a more serious problem. When online the fonts in drop down boxes are so small as to be almost unreadable. On the Google start page the "Google Search/I feel lucky" text is very small as is the text when I type in the search box. I thought this was a browser problem until I came to use Excel today and found the column widths had closed right down and the column letters and row numbers were very small.I have checked in "Advanced Appearance" and all the settings seem correct. The computer is not one I normally use but it seems to me that the whole appearance of the display is rather unusual, but this may be because I am used to XP.