This applies to the Platinum Penta
There is a fuse in a holder on the back of the Penta which may have blown. You can lever the holder out with a flathead screwdriver. Check the fuse to see if it is blown and, if it is, replace it with the appropriate fuse (click here to see which fuse you require).
Make sure you replace the fuse holder so that the arrowhead points to the correct supply voltage.
If this does not solve the problem then check the power cable is not faulty (try one you know works).
If the unit still does not power up then contact the distributor for your country to arrange for your unit to be looked at by an authorised Focusrite service engineer (contact details can be found in the distributors section).