Flashing CAPS and SCROLL lock

Dear all,

I own a Vostro 1200 and run Debian 5.0 (Lenny) on it.  It boots fine and usually is well behaved.  But occasionally, the keyboard and touchpad stop responding and there are two blinking lights: CAPS and SCROLL lock. The only way out is to hard reboot.  After which, it usually again behaves normally.

There is no mention of this scheme of lights in my user manual's "Diagnostic Lights" section.  Does anyone know what it means?

Thanks in advance,

Nishita