You didn't show all your code so we have to guess what else you did. For example, you probably have
found = "false"
before your loop.
It would be better if you use boolean values rather than strings for that. If you used booleans then you would have
if not found:
If you used
read = readlines ()
then, after you use split (","),
details  will include the newline character and that could be your main problem.
You don't seem to be using current except in one place, so you could use
if password == details [index + 1]:
However, it seems you don't even want to do that. You should probably have
if details  == username:
Because details is re-created for each line of your input file, so then you would just have:
if password == details :
and not use index at all. And, if you didn't get rid of the newline earlier, you could strip it with
if password == details  [:-1]:
In Python, it is important to show indentation (which Y!A removes) so either use "... " for each indentation level (with a blank space between each level), or use #end comments to delimit blocks, or use a code-posting site (ideone.com, codepad.org) and post the link here.
I've been assuming that you saved your sheet as a text file -- something that can be done with Excel.