Sleep option disabled on XPS 1340 running Windows 7 x64

The sleep option seems to be disabled on my XPS 1340 when running Windows 7 x64.  This means that closing the lid does not sleep the laptop and I have to be careful as it can easily overheat.  I really need to be able to get sleep running again.  I updated to the latest Bios, and installed the nvidia drivers (Dell doesn't have x64 video drivers).

Here is the output of powercfg -a

The following sleep states are available on this system: Hibernate
The following sleep states are not available on this system:
Standby (S1)
        The system firmware does not support this standby state.
        The VGAPNP.SYS display driver does not support standby.  Please consult
your hardware vendor for an updated display driver.
Standby (S2)
        The system firmware does not support this standby state.
        The VGAPNP.SYS display driver does not support standby.  Please consult
your hardware vendor for an updated display driver.
Standby (S3)
        The VGAPNP.SYS display driver does not support standby.  Please consult
your hardware vendor for an updated display driver.
Hybrid Sleep

This seems to point to the video driver (the standard VGA driver).  What can I do to get a real video driver for this system that will not block sleep mode?