It may not be your keyboard. It is highly likely that your computer is busy processing some application requests. I had the same issue on a computer and it had some poorly written security software loaded that was taking all processor cycles and keyboard response was slow. I stopped the application from running and the system response returned to normal. I replaced the software with a better behaving application. I would recommend starting the computer in SAFE mode and see what applications are in Startup and the RUN registry keys. It could be that your computer is infected with some malware (e.g. spyware, trojan, virus) that needs to be cleaned. Try Microsoft’s Malicious Software Removal tool.
Also you can try a Live CD (or USB key) Linux or Windows based. On the Linux type I do prefer Knoppix or Puppy. On the Windows side my preferences are BartPE (but a bit clusmy if tuo have to build it) or UBCD 4 Windows. Using any or all of those live CDs you can be sure that it is not a hardware issue if keyboard works just fine. But as early mentioned just the safe mode could tell.
If it is not a hardware issue, as it looks, you can safely disable any start-up programs and services using the msconfig utility that comes with Windows or better yet download the very useful app autoruns from the Microsoft website. Then disable app one by one re-enabling them until you find the offending one…
A virus scan can also be helpful. UBCD4Win has anti-virus soft that can be run from the CD or USB flash drive.