If it is a work computer, then it may only be relying on integrated graphics, like my work PC. Integrated graphics only support 1 monitor. In order to be able to use more than one monitor would simply need to install a graphics card. Any graphic card will support 2 monitor; up to 1920x1200 resolution per monitor. A Radeon HD 5450 is very inexpensive and is fine for any office work that is not graphically intensive. If your "office work" means rendering 3D graphics, then something hugely more powerful and expensive would be recommended. But for spreadsheets, databases and video conferencing the Radeon HD 5450 will do fine.
You should be able to find a Radeon HD 5450 at Newegg.com for around $15 - $30 after rebate. And installing a...