Lego RCX 1.0 problem with communication
Try to use this (Windows XP x86):

RIS v2.0 software -> http://www.mediafire.com/download/vrg2iajcv4uxkf3

Updated USB Tower drivers -> http://www.philohome.com/sdk25/tower164.zip

Also maybe you have a faulty RCX or IR tower. Try to change the battery of the IR tower.

I recommend the use of the Windows XP x86 (32 bits) for install the RIS v2.0 software. You have to uninstall any QuickTime installed in the PC and install the QuickTime that comes with the RIS v2.0.