As following How To Schedule Tasks in Windows XP

I have scheduled that firefox and task manager are to run on startup, and up until now it works, but lately they haven't been running. I checked the scheduled tasks utility and they are still there, unchanged, so I don't know what would have happen to make it stop working?

Windows XP SP3

AMD Radeon HD 6850 - 1024MB

MotherBoard:
ASUSTeK Computer INC. P5K SE Rev 1.xx
Bus Clock: 200 megahertz
BIOS: American Megatrends Inc. 0401 07/19/2007
Realtek Onboard Audio

3328 Megabytes DDR2 RAM

Processor:
2.00 gigahertz Intel Pentium Dual
64 kilobyte primary memory cache
1024 kilobyte secondary memory cache