Streak on screen

I have a MacBookPro with OS 10.8.2. For the first time, this evening when I boot the laptop, there appears on the display, after the initial Apple image but before the sign in screen, a "streak" of pixelated (?) color across the screen. I have posted a photo of it at Untitled Document. The streak appears only then, on the screen between the initial Apple image and the log on screen, and when I log on, everything functions normally. It started to appear after I tried to log onto HBO Go while the Mac was connected to my TV. I have done it successfully numerous times (after getting instructions from this forum, for which thanks again). I say "tried" because this evening I was unable to log on to HBO Go. The Error message I got is "Fatal Error: Failed to load service error definitions". Later, I tried logging onto HBO Go on a desktop with Windows 7 (not connected to the television), and that did not work either. HBO Go simply did not open. I don't know if the HBO Go event created the streak, but the streak did appear after trying to log on to HBO Go. I will much appreciate any thoughts. Thanks.

Try resetting the PRAM on your notebook. Hopefully it's a temporary glitch created from having your MBP connected to the TV. See the following Apple KB article: LINK

YOU FIXED IT!!! I followed your link, and the instructions there, and the streak has disappeared.

Please excuse my shouting, but I was really afraid I had permanently damaged the display.

Thank you for your help.

You're welcome. Sometimes the machine will retain "glitches" in its memory. Resetting the PRAM clears that out. Have fun.