well this almost definitely has something to do with your screen's/graphics card's driver or module...did you check that you enabled/build into the kernel the module that's needed (if there was one) for your graphics card? I mean, for example nvidia cards need a certain module to work, so it must be either in the kernel or compiled as module (which will then have to be modprobed).
another thing is, that if you need a software driver for the gfx card you have, you must install it after kernel update. if you do need one, and compile a new kernel, your X won't work on either the old nor on the new kernel...
check out the module thingie and the driver, if you happen to need one (my nvidia needs nvidia's driver).
modules available can be listed like this:
modprobe -l | less
or to find something specific:
modprobe -l | grep <keyword>
where <keyword> is something you could identify the module from...like in module "usb-uhci" the keyword could be "usb" (without quotes) so that grep would print only the lines with usb -letters in it...so from the module list you get, see if there's something you might need (which isn't already in the kernel; type "lsmod" without quotes to see loaded modules)
when/if you find something, try it:
modprobe <modulename>
where modulename is the filename of the module, but without path or file specification...like /path/to/modules/usb-uhci.x would be loaded via "modprobe usb-uhci" (w/o quotes, again)
looooong explanation...might not work, though.... :P but try.
EDIT: if you missed something in the kernel, and have not deleted the sources, just cd into the source directory and do again
make menuconfig
(or whatever config you used) and check out what you might need, recompile, reboot and enjoy
if you did delete the sources, just unpack them again, run the configuration from the beginning, compile & boot....but you must know (at least somehow) what you might need in kernel.
