Hi, Donata,
The search feature, unfortunately, doesn't use the fuzzy logic of, say, Google...which means that it's often a toss-up whether you'll find what you're looking for or not. But here are a few ways you can increase your chances of finding what you're looking for:
1. Always use the "advanced search" link under the search box. The basic search is so broad as to be almost useless.
2. Try to remember some unique (or at least uncommon) keyword in the sought-after post. It doesn't have to be the actual topic of the post...just a word that you remember from that post. For example, if you're looking for a post that was about some meditation technique and you remember the author mentioned in passing that she often felt surrounded by turquoise light when doing the light body exercise, search on "turquoise" rather than "meditation."
3. If you're sure the post was made by a particular person, you can add the author's name in the appropriate box to narrow the field.
4. If you know the post was in a particular forum, you can specify which one to look in. You can also select a category, e.g., "OBOD Members-only forums" and click the "search subforums" button to bring in all the grade forums, etc. Combining this with an author search can help a lot.
5. If you're certain the post was the first in a thread, you can narrow the search even further by selecting the option to search only first posts.
6. You can also use the wildcard * to bring in partial matches, i.e., if you think you're looking for a post that contained a word along the lines of "luminescent," "luminous," "luminary," etc., but can't remember which, you can search on
lumin* and catch all of them. If you were to enter
*lumin* you'd get "illuminate," "illumination," etc. as well. Of course, you'd also get words like "aluminum" and "voluminous" so it's no guarantee of really reducing the possibilities too much!
7. If you are pretty sure the post was made fairly recently, you can limit the searches to the last year, six months, week, etc. by clicking the appropriate button on the advanced search screen.
Now, whenever you narrow the field, it increases the time needed for the search, so don't think it's locked up...it's probably just thinking hard.

If you don't find what you're looking for on your first attempt, change one variable, e.g., author, forum, or time-frame, and try again. Keep trying until you find it or decide it isn't worth any more effort!
If doing any of this seems more trouble than it's worth before you even start, you can try this short-cut, which may or may not give better results, depending on what you're looking for: Go to Google, enter this in the search box:
site:druidry.org/board/dhp, then type in the word you think you're looking for (e.g.
site:druidry.org/board/dhp illumination), and hit Enter. It will return results only from the public forums, but at least you get the benefits of Google's far-more-intelligent search engine and speed.
Hope this helps.

Edit: Dryadia, I just tried it with "robes" and it worked fine for me, but if you try a search on a really common word—even if you specify an author—it won't even make the attempt. Recently someone was looking for a post Philip had once made and I tried to search for posts by him containing the word "love." No go. (I finally found the reference through the Google site-search on the main OBOD site.)