If you feel you need a more powerful computer because it seems to be running out of steam, there are many ways to achieve this, including:

• Unclogging.  Ensuring that unnecessary programs are not running in the background and stealing "horsepower".   There are many programs that you might have installed (or viruses that installed themselves) which might have set your computer to start up one or more of their modules and run them in the background while your computer is running.  On average, 50% of these are unnecessary and are merely clogging up the works.
• Upgrading the "weakest link" - perhaps more memory, or a larger hard disk, or even a faster processor.  The weakest link can be upgraded for a fraction of the cost of purchasing a new computer, and deliver all the extra power you need.   (Most new computers are capable of doing far more than you would probably need, and you would be paying for this.)
• Adding a new component - perhaps a CD-ReWriter, or a DVD player, or a better sound system, or more USB ports to accommodate cameras, scanners, and other attachments.   All of these components are relatively inexpensive and are unlikely to require much, if any change, with respect to upgrading any other part of your computer.
• Refurbishing.  If you are quite happy with your printer, mouse, keyboard, floppy disk drive, monitor, and other attachments, then you can acquire just a new "box" containing a new motherboard, processor and memory at about half (or less) of the cost of a complete new PC package.  Your existing hard disk would be transferred to the new box, and/or a new, larger, hard disk could be added for little extra cost.
• Disk Storage Expansion.  If you need to increase your disk storage capacity, then adding a second disk, rather than replacing the existing one, often provides a better foundation for overall disk performance and data security and backups.