Do you have anything plugged into the laptop? If so.. try disconnecting them and see if this problem continues to occur.
If that doesn't work, then does this happen with "any" user? Try making a new user and see if it affects that one.
Also... do you hear any signs of disk activity? I did some Googling on this, and in some forums there was speculation that the system is merely tied up doing a Spotlight indexing, for example. Someone also said they were able to recover from this "lockup" by holding down a key for several seconds.
One near-sure way to see if this is hardware or software is to create a new partition on your system and do a clean install of OS X onto that partition and make a new user on it (don't migrate users, don't install any other apps). If you boot from that "clean" partition and continue to have troubles, then it's a near-certainty that the problem is the hardware, or less likely a bug with the OS and that particular machine.