I've turned my HP 95LX on but the screen is blank.

It is likely that the main batteries are low and that the HP 95LX is being powered by the backup battery. The backup battery will maintain your data for a few hours but is not strong enough to display data on the screen. Either plug into an AC adapter or change the main batteries as soon as possible. If it is not a power problem, you can try a hard reset, see page 1-13 in the HP 95LX User's Guide. If this does not work contact your Service Center.