no admin rights- windows 7 os

You cannot change the date and time or it asks yes and no when you try to change any system configuration? if it asks.. it's default OS security. It is called User Access Control (UAC).. After Vista onward Microsoft start asking permission if user making any changes and it asks for admin rights.. it's normal. you need not to worry.. you can change this asking permission dialogue from your control panel.. go to control panel and search for UAC, you will find option is checked to ask User Access control.. you can uncheck and restart your computer.. :-)

The first thing I would ask is did the "service centre person" install a legitimate copy of Windows 7? Did they charge you correctly for the upgrade and give you the CD and Licence Key? If you get error messages when trying to change things like date and time and cannot access the Control panel, then they have installed a 'locked down' version - that is, with some rights disabled - this is very often done in corporate situations where a user is given a laptop or a PC by the company. The Windows licence used in this situation is generally a multi-user licence which is owned by the company and not by the individual and the installation is modified to make it easy and quick for IT staff to install Windows with specific limitations. "Admin mode" is a misnomer because access to certain functions has been disabled. I think that, since you had the work done by a 'service centre' (and presumably paid them), you must take the PC back to them and insist that they correct the problem and give you full access because they have clearly given you a copy of Windows 7 which you don't own (and have probably done so 'on the cheap'). In other words, you were misled at some point and have been ripped off: you DON'T own the copy of Windows which was installed unless you have a proper Microsoft holographic label (either as a sticker on your PC or as shipped with the DVD which they should have given you).