New Set Up issues

I am setting up for the 1st time. Pi 400, 64gb micro SD, 1TB SanDisk SSD (only powered by USB). I followed micro sd card programming instruction and get the prescribed quick green flashing light on the key board and green screen on the monitor. Then I have flashed the getchannels image to my 1TB drive, but when I reboot (having removed the Micro SD card) with the 1TB SSD drive connected I get a repeating error image. The green light on the keyboard is solid.

It doesn't see your ssd attached.

thank you. I used a different USB external drive, and now I am installed. I am now figuring out how to use it. Tried to connect to Xfinity (subscription at my 2nd home) with out success. Is there a good step by step guide?

I would recommend reading the dedicated Xfinity TVE thread.