This achievement is a pain. Always look for blue and yellow cases on the wall each one has a power node guaranteed. Do not sell your weapons, you will lose all upgrades you bought for them. You will need to do multiple play throughs on the same save. You can purchase power nodes at the store for 10,000 credits each, so be sure to save up your money. Concentrate on stuff you need first then move on to weapons you don't use. When you want to upgrade go to up to a work bench and press A, then select what you want to upgrade and start popping in power nodes for each upgrade slot. 155 Power nodes needed total. You do not have to waste them on the empty slots, try and go around them.