[help] external hd files got lost

Hi. im not quite good in terms of virus.. i dont know what happen to my external HD... ive saved all of my important files in my External but after ive connect it to other computer(neighbor) and when i connect it to my computer my files got lost and maybe hidden..but still the capacity of the external didnt change (external space is 500GB without file and my recent space available now is 282 GB so it means there is a file there) but i cant see maybe it is hidden.. i dont know how to recover it and i dont know what to do to get it safe ... My computer dont have anti virus but im using USB Disk security.. and now im installing microsoft essential to protect my remaining files in my PC...

sorry for my bad english.. Please help me BHW..

thanks


PS. im using windows 7 OS.. 32 bit

please help friends from BHW.. thanks in advance.. its a big help for me for any suggestions that will be given here..

1) Use some free partition manager (search exactly that phrase on G) to see did you have hidden partiotion or something
2) use some of free UNDELETE software (also use G to find)

3) even if file is DELETED you will recover with un-delete software

how to search it? is there any commands or do i use RUN for that? if yes ? how?

still not fix..any one can help me now? please