Looking annoyed with your system and wants to replace it! Right but do you have checked you system thoroughly to diagnose the core problem of your system. If your computer is creating problem them simply replacing it is not the solution of the problem. You must be aware of the root cause then you can make a solution. First of all give your computer a trial and check where problem is. If your system is working in slow manners, check the data storage and delete all the unnecessary files to reduce the load.  

Make sure that all the programs in your system are up to date and running in correct manners. Installation of too many software can also affect the working efficiency of a system. Antivirus is an essential part of computer programs. Run a reliable antivirus to keep safe and secure the data stored on the hard drive. If the problem still persist and there I no other option then replacing it, you can look for a new system or you can make your existing system a new by adding or replacing the hardware or other computer components that are inevitable to change. 

Here you have two options either to buy a new one or get a used hardware or other components such as used etc on discount rate. You can buy all these equipments online from CiscoDealer.com having a huge inventory of all used Cisco systems including used Cisco switches, cable, memory, IP phones etc.