My wd elements 1tb is running slow

i used to play everything from my external hardrive but since yesterday every takes ages to load eg games 

Run a quick test with DLG, if it passes the test, backup your files and format the hard drive. If the test fails replace it. Check the link below for the steps.

You can also try to do a backup of all your data, install Hard Disk Sentinel and try to do a surface test to see if there is some problem with the disk, and choose reinitialize disk surface to see if the values of transfer get any better.