I have an external portable Maxtor basics 500gb removable drive with me now its not working ... and it is not detected in the operating system as well as in the BIOS settings ... what can i do now.

First make sure usb cable is working fine. Go to bios for that when you power up the computer press F1 or F2 or del or ALt+F2 key to enter in bios then go to advanced option and enable legacy usb then save settings and exit from bios. Also follow below for windows os First make sure usb cable connected to harddrive is working fine.
try it in different usb ports.
Press windows key +R key so you can see run then type in run "devmgmt.msc" then press ok so you can see device manager uninstall all usb drivers then it automatic install usb drivers.
then check.
Also you need to change registry for that type in run "regedit" then press ok then you can see registry editor then locate below key.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E965-E325-11 CE-BFC1-08002BE10318}
And remove upper filter and lower filter.Then restart computer then check.
Try your harddrive in different computer if it is not recognized on another computer too then your harddrive has internal issue.

Let me know if you need further assistance.
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