Having just got my Raspberry Pi operational I thought I'd cover some video related issues and how you might sort them out too.
Firstly, I plugged everything into my Pi and didn't get a picture (even with SD card done, lights on etc).
So, I opened up a DOS box on my PC and pinged the new IP address that my router showed, so I knew it was 'on' and the SD card's OS image was operational.
Then, I realised that the HD TV and HDMI cable I were using had never been used/proven to work. By swapping inputs/TVs/cables I fault-found the right TV with the right input using the original cable. I could have used a DVD player as a way to prove the connection, but I didn't need to in the end.
Right, now I had a picture on the screen (or rather a scrolling cascade of white text on a black background as the Linux OS displayed its boot-up sequence diagnostic information). However, due to my TV trying to show things in widescreen the screen was clipped on each of the edges. This is common on a lot of TVs, where losing some of the picture at the extremes of the edges is part of how their formats are altered. Unfortunately, this means you might not be able to read all the words/see the whole screen.
In my case, I couldn't see the bottom line, so although I suspected that there was a login prompt just out of sight I wasn't sure. Hitting return a few times at this point caused no harm and confirmed this. So (as I was using Debian) I just typed in pi <return> then raspberry <return> to login. Hitting <return> a few times again proved that my login was successful.
To then get the graphical interface going just use startx <return>.
This should get the GUI visible and it might be that your TV correctly synchronises to the video it is getting and your problems are solved. Turning the TV off and on can also sometimes get it to make a better guess at things and improve the display.
In my case, I still had the 4 edges of the screen missing. To get things started I moved the mouse cursor off the bottom left screen corner and left/right clicked until I hit the panel controls dialog. This meant that I could enlarge the panel bar to be larger and therefore visible so that I could proceed. You can also move it to the top or one of the sides if this helps.
Ultimately, I found the full answer to be in my TVs more obscure settings. For me, on my LG TV, changing the aspect settings from 16:9 to 'just scan' gave me the full picture. In this case, this made my TV change its screen view to match the incoming video from the Pi instead of trying to preserve the 16:9 ratio favoured by Sky boxes etc.
I hope that helps.