This has nothing to do with your overclock or your card's drivers. The issues are with punkbusters compatabilty with 64bit windows 7 and your realtek sound drivers. Myself and many others have had this issue, just follow the directions on the link or below.
Allright, this seems to be the solution for my Hardlock. Here's the full description of what i did, and it is only related to users who run on Windows 7 64-bit, and probably have a Realtek soundcard.
1. Download pbsetup.zip.
Unpack it onto your Desktop, or anywhere else you like.
Go to step 2.
2. Go to C:\\Users\\<username>\\AppData\\Local\\PunkBuster\ \BC2\\pb\\ and delete all files from there.
Then go to D:\\Games\\Battlefield Bad Company 2\\ and remove following files.
Go to \\pb\\ folder and clean it too. Warning, this will "forget" your login data, if you checkd the "Remember me" box in the game, so make sure you remember your password.
Go to step 3.
3. Go to C:\\Windows\\SysWOW64\\ and locate PnkBstrA.exe and PnkBstrB.exe.
Set compartibility mode to Windows XP, and check the "run as admin" box. Do it for both files.
Go to step 4.
4. Run pbsetup.exe, add you game and update it. Don't forget to run it as admin.
Go to step 5.
5. Open PowerShell (run as admin!), and type cd c:\\windows\\system32 [Enter] sfc /scannow.
Reboot when completed, then go to step 6.
6. Open the PoweShell again and type cd c:\\windows\\syswow64 [Enter] sfc /scannow (make sure you ran the 64-bit version this time).
Go to step 7.
7. Kill the lag spikes!
8. Try to play the game, if you will keep getting hardlocks, try to install the latest realtek driver and set sound quality to 16 khz, and reboot.
If you still keep getting hardlocks (pc freezes, with Brrrrrr sound), try to Uninstall PB using pbsvc.exe (could not find the correct version on evenbalance), Reboot, Install PB, reboot again, then take steps 1-2-3-4 and reboot.
I haven't had a single hardlock since i've done these steps. I've had a CTD, but it was ATI-related.
If you use ATI, try to disable ATI A.I, as it causes texture and screen flickering for some users. If you don't have this issue, go along.