a box keeps popping up saying "login to iCloud" but won't let me login. it keeps popping up

What do you mean it won't let you log in? Does it say the password is invalid? Or the email address is? Or something else?

Please post ascreenshot of the dialog box requesting your iCloud password:

To take a screenshot hold ⌘ Shift 4 to create a selection crosshair. Click and hold while you drag the crosshair over the area you wish to capture and then release the mouse button. You will hear a "camera shutter" sound. This will deposit a screenshot on your Desktop.

If you can't find it on your Desktop look in your Documents or Downloads folder.

When you post your response, click the "camera" icon above the text field:

This will display a dialog box which enables you to choose the screenshot file (remember it's on your Desktop) and click the Insert Image button.

⌘ Shift 4 and then pressing the space bar captures the frontmost window.

⌘ Shift 3 captures the entire screen.

Drag the screenshot to the Trash after you post your reply.