Today was the first day i've really had to fiddle around with the Pi since its arrival.
I had been keeping aside an old (ish) 19" monitor to use with the pi and had briefly tried this the previous day, only to find that the screen was severely off to the left hand side, meaning I couldn't see the prompt properly and when running xwindows, the start button (for want of a better word) wasn't visible.
So, first thing to fix. I feel that I need to say that I ended up using a different monitor as I couldn't completely solve the problem to my satisfaction, but I hope that some of the steps I went through are helpful to other people (and also I couldn't really justify a fourth monitor on my desk)
There are a number of threads around on a file called config.txt. This file is used as part of the boot process of the Pi, which actually boots from its Graphics Processing Unit (GPU), the config.txt file is first read by the GPU before the ARM core is initialised. The Pi is supposed to negotiate with the screen to get the correct resolution, but if it doesn't then you can force screen settings (and other settings, although this are more risky, such as over volting).
If you are having screen problems it is always worth trying a different HDMI lead, many are of dubious parentage (one of mine cost 37p) so my feeling is that this is the first way to go. I tried this and still the same, so onto the config.txt file.
In my case, this file didn't already exist (it is optional) so I had to create it. There are two main way to achieve this, both of which I will detail:
1) This method is from the Pi itself and I am presuming that you have already started xwindows. If not and you find yourself at a rather unfriendly DOS type command prompt, and it is asking for a username and password, the details for debian are User: Pi and Password: Raspberry. Once you have logged on, type 'startx' to go into a windows type environment. Now, if you can't see a start type buttons as on windows, you may well be having resolution problems. From the keyboard, try hitting CTRL & ESC keys together and hopefully this should bring up a menu. Go to Accessories and then LXterminal.
This will bring up a DOS style window and a prompt that looks like this: pi@raspberrypi: at this prompt, type sudo nano /boot/config.txt - Sudo is a Linux term that means you are using admin rights (more possibly on this another time) Nano is a text editor and config.txt is a text file in the boot directory that we are going to edit (if it already exists) or create (if it doesn't)
Now, i'm not going to list all the different modes here, they are available at the Raspi wiki here: http://elinux.org/RPi_config.txt DO NOT be tempted to play around with the voltage settings, as this will invalidate your warranty.
Once in the text editor, add in commands that you think may help, each to one line like this: (# character means the line is a comment and will be ignored)
#Set HDMI mode to 19 (720p 50hz)
Now hit CTRL & o (writeout = save the file) this will prompt with the path of the file, just hit enter again. Now CTRL and X and you have exited Nano. Now type exit and you will close down the window opened.
2) To achieve the same on windows, take your SD card with Debian on it and insert into a card reader. Once it has been detected, then open the SD card. There will a a few strange looking files, if there is already a file there called config.txt, then click on it, if there isn't then right click, create new text docment and call it config.txt. Open it up and add in settings as per above. Eject from the PC and put into the PI
It should go without saying, but never remove the SD card, or insert the SD card into the Pi when it has power applied to it. Always make sure it is unplugged from the power supply.
Following a lot of experimenting, non booting after changing settings (if this happens to you, get the SD card to a windows PC and comment out the changes you have made, and the pi should boot normally) I discovered another thread, that suggested downloading a newer 'elf' file from this address: https://github.com/raspberrypi/firmware/raw/master/boot/start.elf This made a lot of difference, the task bar and buttons were more or less on screen. However, the more or less part troubled me and again it was going around with changing settings, booting, seeing what happened and trying again.
Eventually, I tried on another monitor and the Pi booted perfectly, first time and with nothing in the config.txt file, so I took the decision to cut my time losses and use the other monitor.
Chickened out ? Probably, but I only have a limited amount of time to play with stuff like this, and fine tuning monitor settings isn't my idea of fun :-)