If your computer is slow right after restarting, you might have too many programs set to open on startup. You should go through all the programs that have opened up and find ones you don't need. Under settings for most programs there is an option to start when windows starts up, which you can de-select.
Your hard drive might be slowing down your computer in 2 different ways: it is fragmented and programs take longer than normal to open, or it is simply too full. Under the hard drive's properties there will be an option to defragment, in which the program will analyze and tell you if you should or not. This may take some time. If your hard drive is simply full, you should upgrade to a higher capacity drive, or invest in an external hard drive to back up saved pictures, music and videos to.
Your computer's ram may or may not need upgrading. Most new computers have enough ram to run all of today's applications, but if you have an older computer that has been upgraded to Windows Vista/7 then your ram will likely be used up. While running all of your normal programs, you can use task manager to check your ram usage. If it exceeds your actual ram, it will use a portion of your hard drive that your programs will overflow onto, which slows things down drastically.
Lastly, a good antivirus program is a must to keep your computer running smoothly, and to keep bad programs from running in the background. I recommend Avast, it is free and works quite well.
I hope this information has been helpful!
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