When you're screening for head lice you're not just looking for live lice. Lice are very, very small and move through the hair quickly. They are often found near the scalp as you part the hair. Lice can detect movement and will hide away from bright lights making them difficult to find.
Part the hair and look near the root for nits stuck onto the hair. Nits are tiny, oval shaped and cemented to one side of the hair shaft. They are not white but rather amber, grey, cream or even black in color.
If you find anything that looks like a nit, you'll need to single out the suspected strand of hair to have a closer look. You can eliminate most debris, dry scalp etc. by running your fingertips (just the tips only - do not use your fingernails) over it. A nit will feel like a bump and stay in place. If it moves when you run your fingers over it, it is not a nit. If it just falls through the hair while you try to single it out, it is not a nit.
If it's still stuck there, try sliding it off the hair again but this time use your fingernails. It may take some effort to make it move, but slide it down the hair a few inches, then stop. A nit will remain stuck onto the hair strand until it is taken off completely.
Check again to make sure that it is oval shaped and stuck to only one side of the strand of hair and not completely wrapped around it. You may want to pull it off completely or cut out that single hair strand. Some extra light and magnification will help you see the shape & color, or you can put it on a white background (since nits are not white, they'll show up clearly on the white background). You can also look for more in the same area as the female will lay a groupings of nits in the same toonie-sized area
Once you confirm the infestation, begin lice treatment and screen everyone else in the household and begin removal as soon as possible to avoid any risk of passing it back and forth