Three's mobile broadband

You can resolve this by:

(a.) Plugging in a USB WiFi adapter to your Dell laptop, or using its inbuilt WiFi capability, OR

(b.) Finding the correct USB mode-switch settings, so that it (your USB device) switches back to being a modem (and not just a storage device).

Some Background:

Back in Windows-land, someone had the 'bright' idea that, as all devices need a 'new' driver, any newly plugged-in device should first 'pretend' to be a USB storage device - and attempt to auto-load the driver (stored for that purpose on the device). Then, when the driver starts up it knows to send a command to switch the USB device back into being 'whatever'.

However, Linux (and in particular Ubuntu) does not need lots of new drivers. More importantly, having a device attempt to auto-load a driver (or any executable code) is plain dangerous - and may also breach security policy and/or be prevented by anti-virus software (or similar protective measures).

Instead Ubuntu (and other Linux variants) provides the 'USB mode switch' function, complete with a large (and growing) list of brands / devices, and the data needed to control them. Unless you are using an unusual (or new) device, a simple update will usually resolve these sorts of issues.