How can I determine if phone or digitiser is dead?

I removed broken glass on screen with help of the numerous guides online.

I didn't encounter any obvious problems with removal.

I re-attached the digitiser cables before adding the new glass just as check but it doesn't seem to be working. Although frustrating, I'm willing to concede to the fact that being an amateur, I may have broken this delicate piece, however before I spend more money on a screen with digitiser I though I'd access the phone through itunes to check it still working. Sure enough my computer doesn't recognise the phone at all when plugged in to USB.

The screen is off (as in physically not just electrically!) but I assumed the phone would connect to my laptop. Am i right in thinking this? I'm just trying to detemine if ive ruined the whole phone or just the digisiter before i spend more cash on repairs.

Thanks