There's a possibility that you are clicking on both mouse keys or your mouse is simply malfunctioning.

Here are a few scenarios,

After you highlight the text you want to copy, you could have mistakenly left-clicked twice which could make the highlight disappear.

Why don't you try using your keyboard to copy and paste on your dell laptop instead?

Here's how,

• Copy: Ctrl+C 
• Paste: Ctrl+V
• Cut: Ctrl+X