Which version of the One? M7 or M8?
What version of the software did you have on the phone before you started?
What version of TWRP are you using?
Are you S-On or S-Off?
If you are S-On - Did you flash the boot.img via fastboot after you flashed the rom?
Did you make a backup before you flashed the new rom?
Does TWRP still see your internal storage, or does it report it empty or 0 MB?
Do you have a PC handy with adb and fastboot set up?
Reach out to me on Hangouts if you need help quickly - check signature.