Which processes can I end to make my computer run faster?

[MARYBOO]

Which processes can I end to make my computer run faster?
I am showing a lot of processes running on my computer.
Where I used to work, we were told to end certain processes that were from previous log-in attempts.
Please let me know if there are ways to know which ones I shouldn't end and which ones I should.
I do not want to mess up anything that is important. Thank you for any help.
6 days ago - 7 hours left for voting
Additional Details
I messed it up. I deleted some of my processes that were under my name. Now that task bar and icons are gone. I only have my wallpaper showing.

I shut the computer down to restart it, hoping that it would reset normally, but I can't get it to come back on. (I am at a local library now.)

I was given my computer by a relative who only used it for games and didn't have the internet.
Whenever you turned it on, it would say, "Operating System cannot be found". You could turn it off and back on again, then it would come on. Recently, I had it professionally "cleaned out" down to my Windows XP after I got high speed internet, to try to get it to run faster. After I got it home, it had this problem. I tried to get it to boot up all evening and the next morning before it finally "found" it and came on. I have left it turned on ever since then. Since I had to turn it off today, I have been trying and trying, but it hasn't worked yet. Is there something else I need fixed, too

[soybean]

How old is this computer?  Can you tell us the basic hardware specifications of it?  What make and model is it?

How many processes are actually running after startup, now that you've "had it professionally 'cleaned out' down to my Windows XP"?

I suspect you may have some hardware issues, possibly hard drive or the internal power supply unit in the computer.

[dahlarbear]

1.  If you expect to use a computer for any length of time, you need the resources and ability to restore or re-install the operating system.  A Windows operating system is a very large complex collection of software.  Over time, it will take some "hits".  Rather than "paying" someone to track down and fix these glitches, I think you will find it more cost effective to purchase the recovery/restore CDs or an appropriate Windows installation CD/DVD for the operating system of your choice.  Learn how to backup your data, re-install the operating system, re-install your applications, and reload your data.  (Or at least have the CD/DVDs available to permit someone else to guide you through the process.)

What restore/recovery or operating system installation media do you have available?

2.  I fear you made a poor choice if you "paid" someone to professionally "clean out" your system down to the operating system.  They should be able to re-install the operating system to a known working state (with or without the data).  Paying them to "fix" or "clean out" an existing installation of the operating system is problematic.

How do they or you know when they've successfully completed the job?

3.  It sounds like "Operating System cannot be found" is the issue you should have addressed.