Excel selecting multiple cells; too annoying!

Majority of times I click on Excel it selects 3-4 cells. I have tried:

1. Turning mouse double-click speed down;
2. ClickLock is turned off
3. Sticky Keys are not turned on.

This is actually becoming too annoying and it is dramatically effecting my productivity. Grateful of any suggestions.

Anyone got any ideas, I'm getting nothing done as unable to select cells .

Very grateful of any guidance?