This question has been answered within Fixya already. Here's what I found.
Over time, and especially when not used, there is a likelihood of dust and old oil forming a sort of glue, or clag....
Remove the needle for safety, then, when you have the setting on Zig zag, gently push the needle arm to the opposite side of the zig stitch.......release the needle arm, and if it springs back quickly, it is fine, if it moves slowly, or almost not at all, then the clag needs removing with application of few drops of methylated spirit to start, at the sort of piston affair that shifts needle arm L & R .....move the needle arm back & forth until it frees up, a drop of oil to finish.........if almost seized, may require leaving overnight after using a penetrating lubricant if it is really resistant....I have had them on the bench for 3 days with manual manipulation a few times each day before they finally come good.
Denatured alcohol is fine, surgical spirit too, different countries have different names or products, essentially alcohol with few impurities that will evaporate quickly with little residue.
Hope this does work for you, tho' as I said, it may take a little time to penetrate depending on severity........the same applies to the reverse mechanism of many machines when they seize.
If you want any more help with this, just post back here, or, drop a line through the "Contact Us" page at www.bargainbox.com.au
I also found this youtube video regarding Husqvarna 2000 needle adjustment. The audio goes in and out-but is also has typed instructions on the video.
Hope this helps.
PS: If you put your question in the "Search problems & products" area at the top of the website, it sometimes gives you answers to your question that other people have also had.