New LED Flat screen Monitor on old PC - Help!

I have a PC (Windows xp) that I bought in around 2003 - 04 not sure which but I think it was 2003 and it had the old big box style monitor. The monitor stopped working this morning and I went and got a new one. The flat screen LED ones.

It keeps telling me the required screen resolution is 1600 x 900 but I cant go up that high. Ive adjusted every combination possible and end up with either too small so that the writing on the screen is all spidery, or it's clearer font but the window is too big for the screen. I suspect it's the old PC. Is this the problem, and if so, is there any way I can fix this without buying a new Harddrive.
ARe there any free download that will fix this? Thanks for your help.:confused

 

without knowing your system specs i would say you need a new video card

 

thanks how do i get one and how much do they cost? What is a video card?

 

Do you know the name and model number of your PC?

 

Thanks. It is MCT Australia.

 

Is this the company?
http://www.hotfrog.com.au/Companies/MCT-Computers
We need a lot more than just a company name. If it was a specially made computer, then you may have to ask the company what hardware is in the computer.