I recently received an email from Bev which at first seemed very strange. She said, "Recently, when I select a portion of text to change it such as bold it, delete it, etc. — the selection won’t hold." At first I thought it was just in Word and figured that possibly her Word documents were opening in "Read Only" mode. When you have a file that is "Read Only" it basically means you can read the file fine but you cannot edit it. This was not her issue since she said that it also happened in email, Word and just about anywhere on her computer when trying to select text. The problem was intermittent; sometimes she could select text, sometimes not, and other times it was a fight to get it to work at all.
I believe it all came down to the mouse, but why could a mouse cause this weird issue? First, it depends on the type of mouse you have.
The older wired mouse with a ball built into the bottom, which is used to track the cursor around the screen, has always caused issues. Think about it, the little weighted ball rolls around the whole time you use your mouse. It touches whatever surface you are "mousing" on. Regardless of whether the surface is very clean or very dirty the mouse ball will get grubby over time. If a dirty surface, the ball picks up dried up coffee spills, grit, toast crumbs, 
etc. Even if it is a clean surface you are still going to pick up dust and lint over time. This collection of grime gets pulled up into the mouse and wraps around the little rolling bars which make the cursor move on your screen. It is fairly easy to clean by turning the mouse over, turning the ring with arrows in a counterclockwise direction, pulling it off, shaking the ball out and with tweezers or a toothpick removing any junk you can see. I do not recommend using a q-tip swab since they can add a few more particles to the mechanics.
What if you have a wireless mouse and there is no ball? Dirt can still get on the little window on the bottom of the mouse, which replaced the ball. Clean it with a lint free cloth or maybe a slightly damp cloth.
Sometimes, depending on which type of wireless mouse you have, the surface you are mousing on could cause a problem. If it is a very shiny or glass surface, try putting a piece of paper under it to see if that improves the action. Sometimes, though not often, it could also be caused by a heavily patterned surface, so check that also.
However, the biggest issue with the wireless mouse and it not working properly is usually the battery. Batteries in the newer wireless mice last a long time. I have a couple that have lasted over a year. Since they are so dependable we sometimes forget about the batteries. So when you have a "tracking" problem like sometimes being able to select text and sometimes not…check the battery. I am pretty sure that will be your problem.
