I understand the desire to 'fix what's broke, 'cause it worked before', but would you be amenable to trying other software?
http://www.techsupportalert.com/best-free-paint-program.htm
There are many, many paint and image editor programs available as freeware.

I don't use MSPaint much at all, but when I need it that's my default- it's just there.

Hope you can figure it out!