I did go for whizlabs for
SCJP 1.4. I downloaded the software from the net and made my payments online. More often as soon as you make the payment, they send you license key (to me they sent it through mail after calling them two times). For activation you would be asked to go online and register with license-key. There you get a file which you would be required to put on some location on your system. Once you have got the file on your system you can activate the s/w offline.
I dont know what did you do but this is the procedure I followed and it all worked fine for me in one shot, (except that I had to call them twice after making my payments...
)
I would suggest avoid,
1. reformatting of the system or
2. switching over to another system and re-installing the s/w there or
3. playing around with the generated key-file.
You can directly ring them, more often it is lack of communication that creates a mess, they do help.