Random number generation

[Awiniki]

I'm working on a stock management system with excel VBA. So far I've been able to add content to excel cells using a user form I created but I'm has trouble generating a random number for my stock id. Here is the sub routine I used. And I get true in the product I'd cell .
Sub random_random number()
For I = 100 to 999
Back:
Rand = Application.Roundup (rand () * 9000,0)
If Application. Countif(Range(B:B), Rand) > 0 then goto back
Else
Range ("B" & rows.count).end(xiup).offset (1,0).value = Rand
End if
Next
End sub

When I equate rand to the active cell which is the product ID cell. I get a TRUE instead of random of number.
Pls what an I doing wrong and how can I generated the random number without duplicated numbers

 

[oldbrewer]

generate a list of random numbers
put 1 to 100 in A1 to A100
put in a random number in B1 to B100 using =rand()
copy col b
edit paste special values
sort by col B ascending
delete column B
you now have the numbers 1 to 100 randomly shuffled