Where did my backup go?

So i decided to update itunes and ios on my iphone 4 using my old laptop as my current one kept giving me an error saying the session could not be started.

when i first connected my phone to my old laptop, i specifically did a manual backup and it took quite a while but was apparently successful. so ahead i go and download itunes and the new ios, install everything and then i get a "an unknown error (-50) has occurred" ARGH! so i click ok, and it wants to restore. except the back up i did is not there?????????? where did it go? have i lost it forever?? the last backup on that laptop was in april, so i've just lost a good 6months worth of apps, data, contacts, messages, pictures etc.

is there any way i can get it back??? please help!!!