Double-click on the My Computer icon.
Double-click on drive C:.
Double-click on windows.
Double-click on system32.
Look for PnkBstrA.exe and PnkBstrB.exe and if they exist, right-click on each one and select Delete.
Double-click on drivers.
Look for PnkBstrK.sys, and if it exists, right-click on it and select Delete.
Restart windows.
Follow the instructions here to reinstall Punkbuster.
Click on My Computer.
Click on the C: drive, or wherever you have Battlefield 2 installed.
Click on Program Files.
Click on Electronic Arts.
Click on Battlefield 2.
Right-click on the pb folder, then click Delete.
Download and run the installation software for Punkbuster, which can be found here.
http://www.evenbalance.com/downloads/pbsvc/pbsvc.exe
Click the Uninstall button.
Close the installer.
Click on the Start button.
Click on Run.
Type regedit in the text field and press OK.
Warning: Changes to the registry can cause your computer to operate improperly, so please follow these instructions exactly as they are written.
Follow these steps to back-up the registry so that should something go wrong, you can restore your system back to a working state:
If you are using Windows 2000/XP/Vista, click on File, and select Export. Note: If you are using Windows 95/98/ME, click on Registry
Then select Export Registry.
Select All under Export Range.
Type backup into the File name field, and click Save. You've now created a backup version of your registry.
Once you've created your backup, continue as follows.
Click the plus sign next to HKEY_LOCAL_MACHINE.
Click the plus sign next to System.
Click the plus sign next to ControlSet001.
Click the plus sign next to Services.
Look for PnkBstrA, PnkBstrB, and PnkBstrK, and if they exist, right-click on each one and select Delete.
Click the minus sign next to ControlSet001.
Repeat steps 5, 6, 7, and 8 immediately above for any other ControlSet folders you have, such as ControlSet002 or CurrentControlSet.
Close regedit.
Double-click on the My Computer icon.
Double-click on drive C:.
Double-click on windows.
Double-click on system32.
Look for PnkBstrA.exe and PnkBstrB.exe and if they exist, right-click on each one and select Delete.
Double-click on drivers.
Look for PnkBstrK.sys, and if it exists, right-click on it and select Delete.
Restart windows.
Follow the instructions here to reinstall Punkbuster.
http://www.evenbalance.com/index.php?page=pbsetup.php
Try to play Battlefield 2

Have fun!
If this doesnt work, i don't know what will. Have fun!