well you could try in WinHIIP to scan and repair if it doesno help i suggest you format the hdd with WiHIIP and install some games for test .if its still doesnot work then try another HDD .
this is the options :
1- first make sure you are using the right patch for HDL like 48bit for hdd more than 137 GB
2- try another NA
3-try another HDL
4-try with another PS2 if you have it just for test .but i think its not the PS2 issue .but just to make sure
5--try to use uLE if it can detect your HDD int HDD Manager .
thats all i can think .
just remembered one more thing is make sure you Set the jumpers to Master or in Cable Select in some type of WD HDD .