I am pretty certain that part is not from you DC25, and sure the other guys will confirm this.
That is from a switch mech, the plastic barb sits behind a panel and the spring is there to keep the plastic upto this level.
You have asked a question relating to your issue, which has been asked so many times, i think you would benefit from carrying out a forum search on the subject.
There are basically 3 possibilities here, reset switch, yoke cable and head motor.
Head motor will spark in a fine uniformed manner, but if it's like an arc welder then its worn out and requires replacing.
The yoke cable on rhs under side cover, breaks causing intermittent operation and this is the usual reason for no head operation. (and most likely)
The reset switch can fail and become intermittent - i have had this but it is uncommon.
Head motor is relatively simple, stu has a video on the forum.
Reset switch is fairly straight forward.
yoke cable is easy for the experienced, but can be a bit daunting for those who are not familiar with it.
If you are lucky it will only need the head motor replacing, but be aware (and many have done this) you can replace the whole head and the fault remains.
Hope that information helps.