More EeePC black screen problems

Just a week ago I was delighted to get my dual boot system working again as I reported here.
However, yesterday the same problem happened again.
What I noticed was that, while in Ubuntu, the screen would go black after a minute or two. However, hitting any key or clicking the mouse brought back the screen again.
This happened 4-5 times and then, when it happened again, it didn't come back on hiiting a key or mouse-clicking.
A reboot brought up only Asus Xandros although there was, as before, a lengthy delay before the screen brightened and Xandros appeared.
I tried the same fix as before but, this time, it did not do anything, even after 8-10 tries.
I read again the forum thread that had helped me before.This time I noticed that many talked about using Fn-F4 to brighten the screen during the boot.
So, I tried this, hitting F4 while holding down F4 during boot. Even so, no brightening occurred and only Xandros appeared as usual.
However, on the next boot, the dual boot Grub menu appeared and I was able to boot to Ubuntu.
Subsequent reboots brought up the Grub screen without problems.
Now, it seems that the black screening problem and non-appearance of the Grub menu is due to a malfunction of the screen brightness function. Why the Heartbeat fix was formerly able to reverse this is not clear nor why it didn't work this time.