HI i lost my cubase 5 dongle,is there anything that i can do and i still have my cubase 4 dongle.
Contact tech support through the form in MySteinberg. Best of luck! 
There is an article in the knowledge base. Here is an excerpt.
I have accidentally lost my USB key! Does it get replaced by Steinberg?
Again, the USB-eLicenser is the most vital part of your product!
Please make sure to have all keys registered in MySteinberg so that the key number is known. Without a MySteinberg account and a USB-eLicenser registration, no replacement is possible.
Now, in case the USB-eLicenser has been lost or stolen, please contact your local support for further information on how to proceed.
It might make sense to have an empty spare USB-eLicenser at hand as we only replace the licenses stored on the lost/stolen key (if all preconditions are met).
HTH
J.L.