[Q] Rooting Help topic

I I rooted my phone and honestly im new to all this. I installed a new lollipop rom released by Oneplus on my oneplus one today, and after not too long got tired of the bugs and my service constantly crashing, so i tried to re install the original ROM but i messed up. Now im stuck in fastboot and my computer discovers the device but i have no os and no recovery mode, any flashing i try to do on fastboot results in a FAILED<COMMAND WRITE FAILED <INVALID ARGUMENT>> PLEASE HELP