Many units come back from service needing work done in the store to be complete. If you look at the agents notes from BEFORE sending it off, it should show a basic hardware check... including the hdd. If not, GS work is garunteed for 90 days. It wil rely heavly on the sheet you signed when you dropped it off. The condition recorded by the tech and agreed to by you should match what you pick up. If not point it out as soon as you can and before you take it home. If you think it was dropped, which I can't really say without inspecting it, but a broken screen is a sign. Actually it it almost impossible to drop it hard enough to damage the hdd w/o breaking the screen. If you still work at the store I would find out who the lead, or best tech is and ask him to give it a complete and extended bench testing. I would forget about windows 7 for now. BB is not allowed to support it as it is a beta version, and the software tools used to repair units does not have support for w7. You can do 2 things to put the tech in a better mood...1) bring your adapter 2) ask the tech how long they need instead of demanding it same day. You'll get much better results because they will have time to do not only the standard things, but I find that they will go the extra step if they know they have time.
You should be given papers from the svc cntr, it should describe not only what they did, but what may be requiered by the store to complete the repair. You should also have papers from dropping it off. Read it all over and make sure you get a good explaination for any unexpected work. Most agents really do want to do right by the client, but you must ask the questions any time it starts to get off course.