Scheduled Tasks not starting?

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

Hallo colintyvu, welcome here.. but please, this Forum speaks german..
Was hast du als letztes vor dem Problem installiert?
Hast du einen Wiederherstellungspunkt probiert?

Hallo, here is a good descriptions how you use the task-scheduler !
but is in German-language .

100. Die Aufgabenplanung oder die Zukunft ist planbar!

Gruß