On so many PCs people simply install hundreds of programs about some of which they have not even an idea. Of-course PCs are for running programs. However care must be taken in choosing and installing programs. Badly written programs can leak memory affecting performance and some programs can compete with some other causing unexpected problems and instability in the system. 

One reason PCs perform poorly and start slowly during booting is because too many programs are loaded in the startup. This can be verified and changes made by usinga program called msconfig. 

You can click “start”, click “run” and type “msconfig”, press enter to get the program loaded. In msconfig go to “start up” meny to check and uncheck programs that are not needed to be loaded during stratup.  

Also, wisdom should be applied when choosing what programs to install on your PC. You don’t want ill written program to be used and then get into more serious troubles.

MSconfig program can do other functions. However it is recommended to constrain your changes to "startup" only. That's because if you are not familiar with what you are doing you might as well land in some additional problems. MSconfig changes can be easily altered if you at any time wish to reactivate a program or make an additional change. This does not have any bearing on most programs working. It simply removes the programs from the startup.

only program which would need to be started and running all the time need to be retained.