I believe it cause by virus. My Outlook express can't be found now. I put it at desktop, now the icon be removed. Checked Crogram files, the folder of outlook express still there, but 12 files(include hidden files) left, and no program application file can be found. and also font setting of some programs are changed. My OS is Win2000, I just download the sp4. I tried scan the virus online at Trend Micro, found and cleaned malware.WORM_NACHI.A but how can I get outlook express back? I even re-installed Microsoft Office2000 Premium already.