Whenever I left click, the client graphics go black for a quick moment.

[I̶c̶e̶N̶i̶k̶i̶]

Open a cmd as administrator and type
 sfc /scannow this will scan for missing or corrupted system files
If this doesn't help I think format and fresh install as teru said is your best bet

[Goldengate]

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.

[WoodEmblem]

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: ).

EpicPerfectWorld.zip MD5 checksum

Direct download/v115 Torrent MD5: 45af004fc471cf590cf34e396ac7d35a (direct download from Europe, American server should be the same)

[Goldengate]

EpicPerfectWorld.zip MD5 checksum

Direct download/v115 Torrent MD5: 45af004fc471cf590cf34e396ac7d35a (direct download from Europe, American server should be the same)

Restore your computer to the original Operating System it came with, they usually have all drivers installed so it should fix your current problem.

[LillySatou]

You're SERIOUSLY gonna need to put a few fans into that machine, you're cookin that HDD!

[Goldengate]

You're SERIOUSLY gonna need to put a few fans into that machine, you're cookin that HDD!

SSDs/Solid State Drives are better than HDDs :3 They don't need any cooling device at all <3