Unable to login to admin

OK, I used my own computer as a webserver therefore I installed PHP5 and Apache2 on my windows XP. Everything runs normally until I tried to find and install guestbook and poll scripts into my website. All those scripts I found uses admin control panel, and of course needs to login. Including the Advanced Poll 2.0.3.

Here is the problem, I tried to login using the correct username and password and it brings me back to the blank login page again! Yes, I'm very sure it's correct (if I typed it wrong, it bring me to the wrong password page). Can anyone tell me what is wrong with it? Any help will be greatly appreciated.

By the way, here is some extra things,
1. I did not use MySQL, all scripts I installed uses text database.
2. Windows XP here, I can't do such thing called CHMOD.
3. Tried using IE6 and Netscape7, same results.
4. No, it doesn't show any error messages.
5. Of all the scripts, only one worked, that's Purple Yin guestbook.
6. It's not cookies and caches' problem, cleared them up.
7. Same problem with another computer (different network too).

*BUMP*

*BUMP*

you might try and read the stickies. About admin login loop. Or do a search.