here is what blizzard suggested. has worked so far
Please try the following the steps:
1. Make sure the latest video drivers you are using are compatible with the latest version of DirectX or you could experience video problems. Contact your video card manufacturer to ensure compatibility if you cannot find the information on the page you downloaded your video drivers from. Make sure you have the latest version of DirectX from
http://www.microsoft.com/directx/homeuser/downloads/default.asp.
2. Make sure you have the latest drivers for your Video and Sound cards. You'll want to check with your computer manufacturer or the Video/Sound card manufacturer's website for the current drivers that match the model of card you have in your system. A list of manufacturers with contact information can be found at
http://www.blizzard.com/support/?id=msi0369p.
3. Download and install the latest chipset drivers for your motherboard. Check the motherboard manufacturer's website for updated chipset drivers, first. If you can't find updated drivers at the manufacturer's website, the next two most common locations for chipset drivers are
http://www.viaarena.com/?PageID=2 and
http://www.intel.com/support/chipsets/
4. Before starting the game, make sure there are no other programs running in the background except for Explorer & Systray. Press CTRL+ALT+DEL to see a list of programs running in the background.
5. It's also a good idea to run ScanDisk and Disk Defragmenter to ensure that your hard drive is operating at optimal performance. You will probably find it helpful to disable your screen saver and power management features before you scandisk or defrag. Sometimes Windows will restart the defragmentation and/or scandisk if your screen saver or power management kicks in.
(Windows 95/98/Me)
-Click on the Start button and go to Run.
-Type in "scandisk" (without quotes) and click the OK button.
-Follow the prompts and select "Thorough" scandisk and let it run.
-This will tell you if there are any problems on the hard disk.
-Click on the Start button and go to Run
-Type in "defrag" (without quotes) and click the OK button.
-Follow the prompts to defrag your hard drive.
-This will make the available space more usable by your programs.
(Windows 2000/XP)
-Open My Computer, and select the local disk you want to check.
-On the File menu, click Properties.
-Click the Tools tab.
-Under Error-checking, click Check Now.
-Under Check disk options, select the Scan for and attempt recovery of bad sectors check box and the automatically fix file system errors box.
-Select yes to schedule after restart if a dialog box comes up prompting you to do so.
-Restart your computer
-Open My Computer, and select the local disk you want to check.
-On the File menu, click Properties.
-Click the Tools tab.
-Under Defragmentation, click Defragment now.
-Select volume to Defragment.
-Click Defragment.
6. Delete the bncache.dat file(s) if one or more exist on your hard drive.
7. Our games run in 640 x 480 with 256 colors. Try setting your desktop to this resolution before starting the game.
8. Make sure all Power Management settings are disabled or turned off. If you have a screensaver, set it to "None" before playing the game.
9. Run the System File Checker to scan for damaged or missing files in Windows by clicking on Start, go to Run and type "sfc" without the quotes. Follow the prompts to check the integrity of your files.
10. Make sure your version of Windows has all the latest updates by checking
http://windowsupdate.microsoft.com.