Since you have done much of what was suggested, it sounds like you have two problems left to deal with: excessive startup programs (which you mentioned specifically), and possibly a build up of old and/or unneeded data on your hard drive.
The possible build up on your hard drive can be checked easily. Find out what percentage of your hard drive is free. You should always have a minimum of 25% of your C drive empty. I aim for 50% because this gives me plenty of "wiggle room." I know that sounds strange, but you really do need quite a lot of space on the drive for Windows to actually operate, beyond what it just takes up in data files. I won't go into details because it would make my post way too long. Research it if you like.
If your drive is full of unused or unnecessary files, the first thing to do is find out what you can safely get rid of. The simplest way to gain space is to remove any programs you aren't using, as has been suggested. You can also transfer any old data files to recordable CDs or DVDs. If you do this, I recommend making two copies of every disk you make before you remove the data from the hard drive. This ensures that if one fails you will have another to retrieve the data from. You can, if necessary, read the data directly off the the CDs or DVDs, rather than keeping them on the hard drive, so mark them in the way that will make the most sense to you.
Then you come up against the more difficult task of clearing out any "junk" files-- things like temporary and old files. Run the disk cleanup utility that comes with Windows, and any other cleaner you have. Beyond that, you will need someone to actually teach you what can and cannot be safely removed. There is actually a lot of junk that accumulates on a system over time. Much of it can be removed. The trick is knowing what to leave behind and what to delete. See if you can find someone locally who is experienced to show you. Don't just delete files because you don't know what they are-- you can mess up your system that way.
I am running on the assumption that you have a system that you know to be free of spyware, adware, viruses, trojans, worms, etc. Any malware is a danger to your system. It will also slow it down a lot. Also, you should be aware that some software you use may be responsible for the problem, or at least be contributing to it. There are a lot of "free" downloadable programs that are not well written. Some of them are adware or spyware by design, and some of them just aren't well made. If you suspect that a program may be slowing your system down, then try uninstalling it for awhile. You can reinstall it if you find out that it doesn't make any difference. In the case of some programs, some people want them bad enough to put up with the problems they cause. If this is your choice, fine, but at least you'll know what you're doing to your system.
The biggest thing for you to do is reduce those startup programs. This is a serious drain on system resources, even if you disable or turn off some of them after the system is finished booting. You will need to do some research for this. The suggestions made are accurate-- you can easily turn those programs off using msconfig. You can also easily mess up your system, so don't just run off and start unchecking checkboxes.
This is going to take some time. Your system didn't get in this state overnight, and it will take a little doing to get it back to the state it was in when you bought it, but it isn't going to be weeks or anything like that. It also isn't really hard. It just takes a little research. The site I like to use is:
There are others. Some of them have been listed already in other posts. Use any or all of them to do the following.
I am going to go into a little detail on this one. It looks intimidating, but don't let it make you nervous. Now is the time to back up your system. It will make undoing any mistakes easier, if you happen to make one.
On the start menu, click on run. In the box, type msconfig. Click on Okay. Go to the startup tab. Have a paper and pencil ready. Write down all of the entries. Make sure you write them exactly-- including the precise spelling. Some of them are very similar. Sometimes only one letter is different. It is important that you spell them right. While you are in there, don't be afraid to take a look. As long as you don't make changes you can't mess anything up. The better you know the startup tab, the easier it will be to make sure your system doesn't get in this state again.
Close the configuration utility (msconfig). You haven't made any changes yet, so you don't need to restart Windows. Get online. Have your list ready. Go to one of the mentioned sites and begin typing the entries you wrote down into the search boxes to find them-- remember to type them correctly. You can read what they are and whether or not they are needed. You might want to make a few notes on your list. If you can't find an entry, try going to your favorite search engine and typing it into a search box.
Once you are armed with this information, you are ready to begin making changes. Open the configuration utility again and start by unchecking the checkboxes next to all startup entries that you know beyond a doubt you don't want starting with Windows. When you close the utility, you will be prompted to restart Windows. Go ahead and do so. When Windows restarts, there will be a pop up dialog box that will tell you that you are in selective startup. Click okay. Once you have made the last changes you are going to make, you can check the checkbox on the dialog that tells Windows not to show the box again. Don't worry about remaining in selective startup. It won't hurt your system a bit.
On any entries you aren't absolutely certain about, the best thing to do is disable them one at a time and try running without them to see what happens. This is the part that can take some time. You want to test them one at a time, so that you know for certain which one to restart if there's a problem.
I think you can take it from there. If you mess up your system and you don't have a backup, don't panic. Boot into safe mode and reopen the configuration utility. Undo the changes that messed things up.
Let us all know how it goes.