Sorry that I've only just seen this.
This could be due to a whole host of factors so I'll try and answer as most comprehensively as possible.
First step would be to try all the available USB ports on your computer and a different USB cable if you have one as I've seen faulty cables cause issues like this in the past.
Please ensure you have disabled power saving mode for USB devices:
In the device manager (Start > Control Panel > System and Security > System > Device Manager), in the Universal Serial Bus controllers section, right click each USB Root Hub, choose Properties > Power Management and untick the Allow the computer to turn off this device to save power option.
If using a Laptop, it could also be worth checking the general power management of your computer:
Go to Start > Control Panel > System and Security > Power Options.
Set the Power Scheme to High Performance (if this setting is not available, click on Show additional plans first). Then click on Change plan settings. On the next page set both Turn off the display and Put the computer to sleep to Never.
Then click Change advanced power settings. In the window that opens make sure you have the following settings:
Hard disc > Turn off hard disk after > Setting (Minutes) = Never
Sleep > Sleep after > Setting (Minutes) = Never
USB settings > USB selective suspend setting > Setting = Disabled
Display > Turn off display after > Setting (Minutes) = Never
Processor power management > Minimum processor state > Setting = 100%
Processor power management > Maximum processor state > Setting = 100%
Please note, not all options may be available.
It could also be worth checking for any available USB/Chipset driver updates for your motherboard.
Once you've done this I would recommend optimising your computer for audio as per the following.
Lastly please ensure that you have installed the latest driver available here: https://uk.focusrite.com/downloads?product=Scarlett+2i4
If you're still having issues after this then please feel free to open a ticket with us directly by navigating to the following link and we'll be happy to investigate further and get to the bottom of what is causing the issue.
Alex Bull // Focusrite Tech Support