Open Synaptic, search for kernel....
Install a "kernel-x.x.xx.x-pclosx.pae" kernel (I'd even suggest the .pae.bfs)
=> don't remove other kernels, it doesn't hurt to have more than one installed
Thus, install, then reboot, and select the new kernel to boot in the GRUB menu... please have some minutes patience (that new kernel will initialize some things for the first time)
If such a new kernel doesn't work, reboot in the "old" one, and test another
(you may remove that not-working one then of course / report it here)...
=> normally, they all work well
But remember to change the /boot/grub/menu.lst again for that kernel (I don't think the adjusted settings are auto copied over - if it's the case, that's perfect of course
) (for your deadline-scheduler)