I think you are using a Windows 7 Home Premium Key with Microsoft Office 2010 and hence it doesn't work (either that I am reading wrong). Assuming you mean sticker beside the battery. Probably I misinterpreted. The Office 2010 product key should be found on a seperate card as given here providing you purchased Office 2010 with the Dell system. You also need to ensure that your product key is for the correct version of office, maybe the trial you have is the wrong version, in this case uninstall it and download the correct version (again in the Microsoft Office downloads lsited below). If you don't have the card or didn't purchase Microsoft Office with your system you may install Microsoft Office 2010 (limited functionality word and excel) from the Microsoft downloads listed below. 
Hi, appologies in advance for my blonde'ness, im not good with computers!!!  Bought my laptop new from Dell in March2010...  Used microsoft office in its trial period, couldnt find the key and its eventually closed down on me...  Anyways, i finds the key in the battery case today, i try to put it in unsuccessfully on many attempts. It simply doesnt work.  Any idea's on what to do? :( x
Product key invalid