Windows 7, 64, Word 2007

Last two weeks Word cursor has a mind of its own
Everything okay for a few seconds or lines and then cursor has somehow shifted to a part of the text nearby and there are half lines partially hidden and black lines, left to right border of page and no less than one full line thick, can be blocks sometimes half an inch thick for half the page and then back to quarter-inch but they go the full width of the page.

Have tried deleting normal.comm

Moving the cursor does not make the errors won't go away but if I save the file it "comes back clean" and works okay for a few seconds and then it happens again.

Any ideas/help much appreciated