green flashing in preview and even after rendering, urgent!

hello, i've searched EVERYWHERE and i can only find this issue from a year ago or in older versions of AE with NO help

i don't know how it happened, im new to even using computer programs like this and it wasnt really like this while i was on the trial but now it's happening in ALL of my projects and i dont know what to do

i have a very urgent project to finish but it flashes in every clip i put in and it's very frustrating

i cleaned my memory and cache and restarted several times but it's

STILL HAPPENING

i really need help.

-in need of service user

to answer some questions:

im working on a 1080x720 composition

all of the videos im using i think are MP4 files

i have cleaned my cache multiple times

there is enough space on my pc

i tried rending as the settings that are already set on rending(AVI.) but it still comes out with the green flashing

I didnt have this problem up until recently

i use after effects CC 2018