Vostro 1500 Randomly Sleeps in Vista

[The Asgard]

Just received my new Vostro 1500 and I seem to have a problem were the vostro randomly goes into and out of sleep. I have installed my own version of Vista and I have loaded all the relevant Vista Drivers. I have disabled sleep in the power settings. I'm at a bit of a loss.

Lost count how many times I have installed Vista with different hardware. Never seen this problem.

Anyone else had this problem?

 

[The Asgard]

Seems to be working ok now since I clicked the plastic over the left hinge into place. May be there is a switch/sensor that detects the lid being closed?