The normal Aero theme can only be used if the service "themes" is enabled (Microsoft). Having Aero enabled will actually give your computer a small speed boost, despite any beliefs otherwise.
You can also try using Disk Check from your hard drive properties and schedule a memory check (should find it just by typing memory into start search). Do these at different times, and this will take some time. This way we can see if there are any surface issues wrong with RAM and the HDD.
Windows updates can sometimes mess things up when you have themes and skins installed (I never recommend non-microsoft themes for this reason). I would try removing it. Might use the free version of Revo uninstaller to do so to make sure all remnants are removed. Also, you might try this:
Safely Optimize Win7
:info: Windows updates are important, I would choose them over a skin
You can look for your startup folder and remove all startup programs (or those that you don't use) from it to save resources.
Make sure you haven't deleted the paging file, thats a bad way to try and gain memory
Don't be messing with services or the registry (or the Bios or anything else) if you don't know exactly what you are doing. Windows 7 is pre-optimized, there isn't any need (other than the link I gave you) to optimize it further. You will usually just end up hurting it if you do (if you don't know what you're doing)
I think because you disabled some services your theme is gone (I think) but for testing now try using the normal aero theme (maybe that skin was the cause of your computer being slow)
