1) you cannot normally connect a pc directly to a "cable connection" You have to have the modem, then a router in between because there are router etc services you must have for it all to work. Sometimes the router and modem are combined in one box. Personally I have separate ones, because sometimes you want to shut one or the other down especially if you have network attached storage eg for media serving.
2) Powerline might not be working because it only works when both ends are definitely on the same phase, and ideally on the same circuit breaker in your home's distribution system. If you dont understand this, you need an electrician.
3)What I suggest is you look for a wifi "range extender", and plug ethernet into that. Most range extenders are push-button (WPS) to the parent router nowadays. any tech shop/computer vendor should have several. I have used Netgear and Belkin very successfully.
4) You could have your home wired with cat 5/6 however depending on how many storeys, construction etc itcould cost an arm and a leg (mine did). And note tax point below.
5) Since your employer is making conditions (why, I wonder) it might be better/cheaper/safer in the long run to get another dedicated broadband connection installed where you need it. - if you are using it solely for work the cost may be offsettable against tax and actually cost you nothing. Get tax advice.
Hope this gives you some new lines of enquiry.