in game client fps lag - not computer related

so i have been playing league for a few years now and i have never had such an issue with the client as i have now. the main issues im having is random fps drops for no reason to the point where the entire game freezes, moving items into different slots and clicking on the minimap to jump to a location causes major lag and drops my fps to literally 1 if it doesnt crash the game all together, if i alt tab during a game the client screen will go completely black making it impossible for me to do anything other than turning off my computer through the force power button, i have uninstalled and reinstalled my client twice, set all of my in game settings to as low as they go and nothing has improved my experience in the slightest. this is making league, a game which i love, unplayable and no longer fun, please someone help me with this problem before im forced to quit league because of riots shitty client and lack of customer support.