Excel drop down validation list not visible

I have designed a work book which contains multiple dependency drop down list. And all of them refer to named ranges in the worksheet. Everything was going fine but yesterday I copied and pasted on row's value to multiple row in the column and suddenly the drop down arrows went missing. Objects are not hidden, no freeze panes. Is it corrupted, now what solution can I have so that it doesn't get corrupted again if its so and why does it get. Its very critical to my process cause around 27 people use copy of the same work book. Appreciate your time.

Originally Posted by sprayprincess

I find this:
http://www.contextures.com/xlDataVal08.html
Hope that will elp you!
Cheers!
Jake

Thank you but I have been through this before posting, am expecting some better options. I mean if it happens often then it may be a problem and I personally have not tested yet whether repairing gives the solution, I will check and see today..