MacBook crash?

I have reason to think my girlfriend's MB experienced something like a harddrive crash today. Upon getting home the macbook was running seemingly fine, but of the two external disks connected, the one with the complete bootable backup was not ejectable. Finding this odd I pulled the firewire cable connecting it which brought the system to a screeching halt. A forced restart using the powerbutton (without the external disks connected) revealed the following flashing icon (see image).
Edit: The mac also makes a strange two clicks right after the standard cd drive sound when pressing the power button.

My conclusion is that the macbook was running off the backup disk all day and the internal disk is somehow corrupted or crashed. Is there any way I can check this before brining it in under repair?

The mac in question is a MacBook CoreDuo (bought in sept. '06).

I have a Powerbook Al G4 available if necessary. Any advice on how to troubleshoot this?

bartelby said:

Try rebooting whilst holding the Option key down.
This should give you a choice of systems, if it can find any...

Click to expand...

Well, that did do something else than previously, but it now just shows the same old gray screen, but with a single lonely cursor sitting there. Nothing to select.

Plugging in the backup disk reveals it as a boot option. I selected it and upon heading into osx's disk utility no internal harddrive is available. Does this signify a definite disk malfunction, ie. bring it in for repair?