The GPUGrid recommended setting is to disable the screensaver. I also suggest you do so.
How many CPU tasks are you running simultaneously, how many are CEP2 and are you using other recommended GPUGrid settings?

[OT]To,

1: Using <report_results_immediately>
2: A small cache-setting
3: Disable screen-saver

I would add,

Don't Install Boinc as a service (obviously not the case here)
Use the swan_sync =0 environmental variable
Free one cpu core/thread for every GPU (dual cards means free two cores)
Increase fan speeds (EVGA Precision or MSI Afterburner)
Don't game and crunch
Don't use SLI
Add <use_all_gpus>1</use_all_gpus> to the cc_config.xml file
On some operating systems its probably better to not have Boinc automatically start (Linux and servers), using a script with a delay is better.
Crunch long tasks only if you have a big card (GTX260 is fine)
- requires the 6.13app and thus a recent driver, which may be an issue for some (but probably not in this case).

Then there is the usual crunching recommendations,
Leave the system on
Disable automatic shutdown/hibernate/suspend/sleep
Set power configurations to keep Network, PCIE and Disks awake.

I would suggest you use 100% CPU time, and less cores, rather than have the CPU stop and start all the time.

When you say the tasks "remain at 0% completion" are you saying that they never complete/get reported, or is it just that Boinc displays zero % complete but the tasks run and complete?

Check the FAQ's for swan_sync.

How is your hard drive doing; do you have Indexing Service thrashing the drive?

Reset the project and then do a system restart:

In Boinc Manager (Advanced View)
Under the Projects Tab,
Select No new tasks for World Community Grid.
Finish any existing/running work,
Click Reset Project

You can Check the Messages Tab for progress. I suggest you Snooze/suspend tasks while doing this. After about 5min, do a system restart.

If that does not sort it then try to install Boinc again, just over the existing installation. Use 6.10.60 from Berkeley.

Probably better to be logged on with Administrative privileges when doing this.

Per chance, do you have any antivirus software that might be preventing the tasks from starting? It's usually better to exclude the Boinc folders from the scan. You might also try to setup Firewall exceptions for Boinc.

d_a_dempsey,

Can you also check the windows task manager when a CEP2 task is running and look for wcgrid_cep2_qchem_6.40_windows_intelx86 to check if the CPU time for this process is increasing?

Seippel