I've never had any problems, are those codes you've made on your own, or gotten them of websites?
Anyway, you can find both game genie and par codes Here
Being an advanced cheat finder, I can teach you how you'd go about finding those values yourself.
(I'm not sure if v 1.5 has a way to search for codes, and if it does, it has options for greater than, less than, not equal to, or equal to before, but I' going to mention how you'd go about finding those values)
1. The easiest way you'd go about doing this, is having multiple savestates, (Don't know if this's supported, but if not, then fine) and save a state, or multiples with powerups, if multiple stats, with different powerups.
2. Next, Start a search, grab the powerup, then use the search engine and enter "Greater Than Before"
3. Get hit a few times, or go to another location, then use the search engine and enter "Equal To Before".
4. Now, load your state, or a different state that don't have that powerup, or another and enter either Less than, or equal to before (Less than if you only have one savestate option to load your previous game before you grabbed the powerup; not equal to before if you got a different savestate that's near a different powerup)
5. Repeat these steps till you've narrowed them down to <10, then test them.