I am using Mathematica 6.0.0 for Students on Windows (32-bit).
I was working on a project this evening, when I stopped being able to enter new lines by pressing Enter. Instead, Enter caused my current cell to evaluate. Shift+Enter caused a beep, which was explained by the message “You asked to evaluate the next input cell after the current selection, but there were no more input cells in the notebook.”
I tried to close and reopen Mathematica. which caused cells to default to not evaluatable. I then did a clean start of Mathematica by deleting the Base Directory and User Base Directory, but the problems persisted. Furthermore, after the initial problem, the font changed from the usual blocky monospace Mathematica font to a Times New Roman-style variable space font (shown below). Output formatting also got strange (as shown below).
Has anyone seen this before? Any ideas how to fix this?
It could be that you have lost/deleted your Default.nb stylesheet in your installation, because this defines the behavior
and appearance of all cell styles including Input/Output cells (as well as Title/Section/Text cells).
One thing I would try is to do a fresh installation in a different location (leave your current installation intact) and
try to launch Mathematica from the freshly installed copy.
Probably either the Default.nb or Core.nb stylesheet was damaged or deleted. The earlier problem with Enter
acting like Shift-Enter would have been a symptom of the problem that led to Default.nb or Core.nb being damaged.
Deleting the Base Directory and User Base Directory was a good idea, but this problem is inside
the Mathematica installation.
Re-installing into a different directory (..\Mathematica\6.0b, for example), or removing the current Mathematica and re-installing,
would be the fast way to correct the problem. The next time you start Mathematica, hold down the SHIFT key as
Mathematica launches.
I uninstalled Mathematica and reinstalled it. The default cell is now evaluatable, and the font has returned to its normal appearance, but Enter still acts as Shift+Enter (while Shift+Enter acts as “evaluate next cell”), and I can’t enter new lines in a cell, which is annoying for defining functions and programming in general.
Turns out is was the NumLock(!) being turned on. With NumLock off, Enter creates a new line. Keypad Enter acts like Shift+Enter regardless of whether NumLock is on or off.
For the record, I am on Windows XP on a Dell Vostro laptop.