WHAT code -2100F for MacBook Pro??

In Internet Recovery, these low negative thousands error messages indicate that your provided Wi-Fi Network is inadequate in some fashion, and cannot be used (for this purpose) in its current state.

Common problems include:

Hidden Network-name

required use of a proxy server to get Internet access

required use of a login page to get Internet access

Use of a login server or certificate to get Internet access

Use of PPPoE in the Mac to get Internet access (typically only applies to DSL)

Use of Fixed IP address rather than good old DHCP

Variance of the time by more than five minutes

Failure of Router to provide workable DNS server addresses, or providing 0.0.0.0 [may produce -2002f]

If you have an Ethernet port, you may in some cases be able to move your Mac close to the Router and connect to the Router using Ethernet.

The higher the number, the more obscure the problem.

Also, make certain the Date&Time and Time Zone are correct within 5 minutes.

You go down that list and eliminate each of the possible cases until there are none left.

are you hiding your network's SSID (network-name) ?

... and so on.

This was a great answer. However, I need to know how to get out of the screen with the triangle and the ! In order to start the computer again. Could someone please tell me what to do to clear the screen and then what I have to do to start the loading process again