I am glad this is a printing forums and not a PC support forums
No idea what PC you have, or what you have on it, but this is aimed at all of you here.
SSD will increase the speed of your PC if you are using it as the boot drive. Having an SSD in your PC as a second hard will increase transfer speeds, and increase the load up of some apps. However if it is not your main hard drive then it will be bottle necked by your main hard drive.
Having your PC full of programs and/or data (files) will not really effect the speed of your PC. However having loads of programs load up when you switch your PC on will effect the speed of your PC. Many programs such as Java, Google Chrome, mobile phone software load up when you turn your PC on. They load up so that IF you do use that program it can load up faster. 70% of the time you will not use these programs, so they are sat around using up your PC resources.
The best way to speed up a slow PC is to disable these programs. Disabling the programs from loading up WILL NOT remove the program from your PC. To disable programs from starting up when you turn on your PC you just need to follow this simple guide.
http://www.netsquirrel.com/msconfig/
Defragging or repairing your registry WILL NOT make your PC faster. However if it dose increase the speed of your PC then then speed difference would be around 0.000001%...
Defragging the hard drive is a great way to speed up your PC.
Not installing paid for over the top anti virus is also a good way to speed up your PC. Having Norton or MacAfee on your PC may cause it to be slow as it is always monitoring your PC. Microsoft's free anti virus program dose the same as the paid for programs but uses a lot less resources.
Scanning your PC for Malware using
http://www.malwarebytes.org/ might find problems that your anti virus dose not find.
ccleaner
www.ccleaner.com is a great program for cleaning out any rubbish in your pc.
All the above links are free programs and direct links to the website.
If you need more in-depth help drop me an email
Jamie@ppcrc.com
Hope this helps.