1) Home+on/off @ 10seconds "bypass the slide to power off" and release only on/off button and keep holding home button till pc recognize its on dfu mode.
2) Force to DFU using Ziphone

Is this two on your possible solution? Or perhaps your on/off button malfunctioning.... For most user, the home+on/off is the easiest and confirm method but i believe there also a lot of them fail this and get irritated. However, keep trying and all the best!!

Yo TS, where are you oh? blend ur iphone already ah?