Restart your computer. If you are still having trouble, try updating the
driver for your video card. Failing that, try start menu>run or Windows key +
R then type winword.exe /r to repair Word.
A buffer overrun means the computer allocated a block of memory to read
something, but what it tried to read was bigger than the amount of memory
created for it. A huge file might do this, but it is more likely that your
drivers are out of date or your Word installation has become corrupt.