If its a work pc, then there is the possibility that IT has things locked down, including the usb ports, but thats only if IT is really paranoid. But you say no mount option shows up, either in the usb settings(From home click menu>phone settings>usb settings) you dont have mass storage selected, IT has things locked down, or the cable you are using is only for charging. Strange yes, but I have heard of other users where they found out that the cable they were using was only for charging.
As a side note, the mouse and keyboard(or even another phone) are very different things so comparing them to plugging in the phone isnt really valid. Though another thing you can try is to bring up the device manager(Right click on My Computer, select Manage, select Device Manager) There from the menu, find the sort by connection. Plug the phone in and see if anything shows up in the device list(Anything red or yellow means something went wrong on the pc). If you dont see anything, expand the device tree and look for the usb hubs and see if anything related to the phone shows up there. If not then something is up with the phone(either something wrong, bad settings, or forgot to select mount).