Power Snatches can be frustrating. Continue with your 4-5 sets but try cutting your reps back to 4-5. Your on track with your rest period, but it’s suggested that power lifts may require even more time between sets; even 3-4 minutes. With this in mind, you should feasably be able to add additional weight and get fully rested for your next set. Fatigue may be one of the reasons for your inability to complete each rep. Also, I will generally instruct a beginner to perform a Hang Snatch before a Power Snatch. The starting position for a Hang Snatch is the same for a Hang Clean w/ the bar right almost touching the top of your knee-caps and hips back, flat back, and shoulders in allignment with the barbell or just a little in front (w/ a Snatch grip of course). Try performing the hang snatch until you feel your form is perfect, then move on to the power snatch. If your attemptine Power exercises, you should be using training plates (10, 25lb. plates the same size as 45’s) to get you used to the level you’ll be lifting from. Make sure your using a olympic lifting bar as well. These have better bearings and more flex in the bar. Finally, don’t forget to shrug the hell out of the bar when you lift.