How do I fix my SSD after installing Yosemite and Enabling TRIM? No boot & can't erase
A clean install is not necessary, you simply need to reconfigure your NVRAM (nvram boot-args=kext-dev-mode=1) to disable the kext signing requirement for OS X.  (After which, you can remove your TRIM enabler and reverse this change or leave it until the next time your NVRAM is changed/resets)  

A very clear explanation of OS X 10.10 Yosemite's new policy with Kernel Extension (kext) signing now being required from the creator of Trim Enabler, as well as simple steps to recover the grey boot screen after TRIM/Yosemite mishaps:

https://cindori.org/trim-enabler-and-yosemite/