Don't feel too bad, "my search window vanished" used to come up on Live Help at least once a day

.
From hearing the "bonk noise" I'll assume that when you press on the search button it still highlights after you clicked it and moved the mouse away? (yellow-ish border around it)... If that's the case then it just went off-screen somewhere.
In-world... Edit menu / Preferences.... Graphics... UI Size slider... drag that all the way the left first and click OK...
Now try opening search again and if you can spot it (or part of it) then drag it over to the top left corner of the corner and reset UI Size back to the way it was (most likely 1.0)
If you still can't see it, then try changing the Resolution next (assuming you're in full screen)... Edit / Preferences.... Graphics... remember what it says right now and then just pick a higher resolution and click OK.
If you're not in full screen, either try going into it and pick a higher resolution, or just maximize SL.
Try and locate the search window again now, if you can see, move it to the top left corner and then reset the settings you changed back to the way they were.
Hopefully you found it by now

. If not, close SL and search (Start / Search in Windows, don't know about on a Mac

) for a file called settings.xml (if you don't have it checked, check the box that says "Search for hidden files"

.
For Windows it'll be in the
C:\Documents and Settings\<UserName>\Application Data\SecondLife\user_settings\ folder usually (or something similar for Vista).
On a Mac it's
Library/Application Support/Second Life/user_settings (Thanks Francesca

)
(There are other settings.xml files in a folder with your SL name, but those are not the one you need, you need the one in the user_settings folder)
At this point you can either delete the file altogether, although you'll have to reset all of your settings in that case.
Or open the file in Notepad (Start / Programs / Accessories / Notepad - drag and drop the file from the search results over to Notepad) and look for a line that says:
From: someone
<FloaterFindRect2 value="

four numbers here)"/>
Change the first two numbers to 0 and 66 so it says
value="0 66 xxx yyy"/> with xxx and yyy the last two numbers as they were, then save the file and close and restart SL and you'll have your search window back

.
(An uninstall wouldn't work, because SL never actually removes its settings on an uninstall so if you did try reinstalling, nothing would actually change)
(Edited to include Mac folder, and cause I found out highlighting still works)