phil, it is possible that this is caused by run down internal CMOS battery. the phone may have lost the boot settings and operating system. Just in case, you can follow the steps outlined here
" 1) Make sure you have Blackberry Desktop Manager installed.
http://na.blackberry.com/eng/services/desktop/
2) On your PC, go to Start > Run and copy and paste the following line exactly (meaning with the quotation marks):
"c:\program files\common files\research in motion\apploader\loader.exe" /nojvm
3) The Application Loader Wizard will appear -- click "Next."
4) In the "Connection:" drop-down menu, you should see "USB-PIN: UNKNOWN". Click the "Next" button.
5) You should then see a list of applications ready to be installed for your Blackberry. Hit Next and Finish. Don't disconnect anything and let the lengthy process finish completely." this info is from [http://geek91.hubpages.com/hub/Fixing-Blackberyy-Mobiles-w-White-Screen-of-Death|here.]
If that does not resolve your issue, try to bridge the solder points on the filters. The diagram is available [http://www.4shared.com/photo/Jn7dmKK6/8520_display.html|here.] Those should of course be the last resort. Hope this helps to get you started. Good Luck.