It's a good idea to take a look at what your variables contain when you find that your code is not working as you expect. What's in $currentlog? What is $hour? It's quite likely that the first 2 entries in @logfiles are '.' (the current directory) and '..' (the directory above the current directory). You probably don't want to open either one of those. Have a look at the filenames you are reading from "/perl/ass/" in the order that they appear in the array @logfiles:
opendir(LOGS, "/perl/ass/") or die "Couldn't open /perl/ass/, $!";
my @logfiles = readdir(LOGS);
print "File: $_\n" for @logfiles;
Enabling warnings is useful, for example it would have pointed out your typo when you set $currentlog (use $logfiles[$hour]
Update: Oh, Win32. Your initial code threw me off because you used '/' in your file and directory paths. I don't do enough Win32 work to help - sorry.