Suction cup does not work on a cracked screen. You will loose vacuum via the gaps in the cracks. Also be patient with the hair dryer. You must not rush that process. The idea is to heat the edge of the glass so that the glue strip under will melt or get soft enough to pull lose. Not to hot and not to cold. To hot and you damage the phone. To cold and the glue wont melt. It must be hot enough to touch with your finger for a few seconds before burning you. Then keep heating all the way around as you work IF you are working slow. The glue will harden if it cools done. I broke many screens before the process clicked in my mind. Now I realise how easy it was altogether.

Good luck