Set focus text filed

i have series of textboxes and when u enter text ib textbox1 then textbox2 is enabled and so on.my problem is when i enter text in textbox 1 and click on textbox2,cursor doesn't apper .when i click once again,then cursor is in textbox2 and i can enter the text.

wht is the problem? why the cursor disappers when i click on textbox2 for first time.

tabindex of textbox is 0.

using asp.net/c#

thank you