Try something as minimal as possible. First:

sudo apt-get install xterm

Now create an xinitrc file for your current user:

echo '#!/bin/sh' > ~/.xinitrc
echo xterm >> ~/.xinitrc
chmod 755 ~/.xinitrc

Check that it looks like the below w/ cat ~/.xinitrc:

#!/bin/sh
xterm

Now, as the same user, try startx. You should end up with a plain black screen, an X shaped mouse cursor, and a (very primitive looking) black on white xterm window.

This is just to check if it is not something weird with the higher level GUI stuff. You can exit w/ ctrl-alt-backspace.

If this is okay, *and you have already done an apt-get update; apt-get upgrade, you could try just reflashing the card, but I think this is unlikely.

In any case, you could also try adding this to /boot/config.txt and rebooting:

gpu_mem=128
hdmi_safe=1

I'm presuming this is an HDMI monitor. Comment out any other hdmi_ or gpu_ lines by adding an # to the beginning.

If that works, have a look at the documentation for hdmi_group and hdmi_boost and experiment. You'll have to remove hdmi_safe first -- there is documentation for that on the same page -- and possibly experiment with setting some of the things that sets (e.g., hdmi_boost).

Try something as minimal as possible. First:

sudo apt-get install xterm

Now create an xinitrc file for your current user:

echo '#!/bin/sh' > ~/.xinitrc
echo xterm >> ~/.xinitrc
chmod 755 ~/.xinitrc

Check that it looks like the below w/ cat ~/.xinitrc:

#!/bin/sh
xterm

Now, as the same user, try startx. You should end up with a plain black screen, an X shaped mouse cursor, and a (very primitive looking) black on white xterm window.

This is just to check if it is not something weird with the higher level GUI stuff. You can exit w/ ctrl-alt-backspace.

In any case, you could also try adding this to /boot/config.txt and rebooting:

gpu_mem=128
hdmi_safe=1

I'm presuming this is an HDMI monitor. Comment out any other hdmi_ or gpu_ lines by adding an # to the beginning.

If that works, have a look at the documentation for hdmi_group and hdmi_boost and experiment. You'll have to remove hdmi_safe first -- there is documentation for that on the same page -- and possibly experiment with setting some of the things that sets (e.g., hdmi_boost).