Available options;
1) Restore Windows 7 back to the original settings and reinstall all corresponding drivers for optimum performance.
2) Download WinMD5 from http://winmd5.com/ and find the MD5 value of EpicPWClient.zip. Then compare it with the original MD5 value which is not given yet (Hopefully a generous person will give it to you because I don't have it D: ).
3) Re-download the client from a different browser. I would recommend Mozilla Firefox or Internet Explorer for that particular case.