We read a similar tale at 7723-6122_102-510824.html .
As we dove in a little deeper we found overlapping security and the speed returned. However freezes are not a good sign. It can point to failing hard disks but given only your story I have to note a prior discussion, the HDD and wonder if the clearing actually removed something important. For example I'm finding folk remove the Intel Rapid Storage Tech app without researching what it does. Or they research it and think it's only for RAID.
I currently have a Dell Studio XPS 16 (Intel Core 2 Duo Processo, 2.8GHz, 1080p HD screen, 4GB memory, 500GB hard drive and Blu Ray Drive with a 512MB graphics card.
However, it takes ages to load up and freezes a lot. I do a lot of multi tasking. It struggles to play 1080p video - not an issue with the internet as other computers run fine on the same network. I have pretty much cleared my whole hard drive of files and there is barely anything there. I have MS Office Home & Student 2007 installed and PowerDVD. I was thinking of getting Adobe Photoshop & Premiere Elements but I don't think it would run smoothly! I have paid quite a lot of money for this laptop (