when 8970 wifi works normally, it will flash slowly. you can see the information in the User Guide of 8970 in page 13.....

well.....that's just a show issue,actually, you have already upgrade it successfully you needn't worry about that

here is the URL of TD-W8960N_V4's firmware download page,download the latest one first. Then use wired connection to finish firmware upload. notice:Unzip the firmware you download,use the "bin" file...

How long does you use 8960 until the problem occurs? Reset the router,check if it will be ok. I guess there must be something wrong with your router,normally,8960 will works fine.