How can I best improve my laptop with 100$?

Buy an SSD solely for the OS. This will dramatically improve your laptops responsiveness. They are expensive on a cost to capacity standpoint but they offer far faster boottimes, lower energy requirements, and they can be dropped with no data loss. An ssd will improve your laptops battery life and make the OS feel zippy again. Although if you don't normally do it I recommend a defrag once a month and a complete wipe and reinstall once a year. With an ssd you don't need to do either of these. For a hundred dollars I would suggest the Kingston 40GB or the new Intel 40GB entry. They both have 100MB/s reads which is about 4 times faster read speeds than your current hd. Think of it as windows being four times faster in anything requiring reading from the disk. Which is quite frankly everything.

Use compressed air to clean it out Download and run spybot Add memory

what you can do is have a tech pull the cooling system out and blow what dust is in it out. Also have them take the cooling fan off the CPU and put more thermal paste on the CPU. This helps keep the cpu cool. Have the tech check all cooling fans in the laptop and make sure that the fans are clear of dust and that they are in fact running. You can also download a reg cleaner from Auslogics and that is free. This will clean your regestry and it will run slighty faster. You should also do a clean of files and do a defrag and scan disk. and see where that puts you. Have the tech check the status of the ram that is in the computer. Make sure the ram (memory) is in good working order. If any are bad, then replace it. Good luck with this.

Go to http://pc-optimizer-pro-downloads.com You can safely clean, repair and optimize your computer. It will help improve your system performance.

Most computer users have been trained that if you want more speed for your computer, then add more memory. Well, this is true, in certain circumstances. But for most of the times, it really is just bad files in your registry files. Corrupted or missing registry files can make your computer too slow. The registry is a main part of your computer's Operating System. With time, as you use Windows and install and uninstall programs, your registry will get congested and full of errors. So your computer could slow down. So, if you can clean it up this problem can be solved.Sometimes you can speed computer up by 300%. To clean up registry,You can download a software called regsitry cleaner---Clean registry,remnant,corrupt files and temp files,history,cookies,etc.. This site: http://www.fix-system.com lists top 5 registry cleaner,you can download and scan for free. Good luck!