Is this the rainbow screen of which you speak?
image

If so, that means the boot files on your SD card are missing or corrupted. The rainbow screen
indicates the Pi is hanging at the start of the boot process. If it’s a case of boot file corruption, you
might be able to fix the boot partition. Either way, I agree with Brian. It sounds like the card is bad, or
going bad, and needs replacing.

More info here: