EDIT: Hang on a minute - I've just re-read your question. An .ashx file, like an .asmx or .aspx file is a markup file, not a code file. You can't use regions in these files. You can use regions in the code behind files associated with them (e.g. the .ashx.cs files) only.
Original Answer: Generally, whenever I get these sort of unexplained odd behaviours in VS2010, I reset all the settings, which normally resolves the issue.
Try Tools->Import and Export Settings->Reset All Settings and see if that fixes your region issue.
If not, it may be related to a bad add-in or extension. Try disabling extensions/add-ins to see if that fixes your problem, alternatively try starting up in safe mode and see if the IDE behaves:
DEVENV.EXE /safemode
Hope this helps.