For some unknown reason (this reason is still unknown until now), my Windows XP quick launch bar will not be shown everytime after restart. I can right click the task bar and make it shown again, but after restart, it disappear again.
The solutions are variable, but no one can solve my issue. At last, by studying this post line by line, I got the issue solved by doing the following thing (actually just one thing):
This is the only useful solution, all other solutions like creating folders, setting other registry keys are all useless, and may potentially damage your system. So just use this one line and no need to try others.