Doesn't the Dell have a restore feature through the Dell entry under programs or such?
Usually they have a Dell partition on the drive.
Anyway,your problems may be due to
1.having to much garbage on your drive
2.too many services or apps running
3.not enough RAM
Start with a good clean,then defrag.
Use Safe Mode if the cleaners will run under it.
You could use F8 on startup or type msconfig.msc in the Run box
or use a little app called BootSafe BootSafe - Makes rebooting in Safe Mode a Snap!
After that stop unneccesary services especially the Indexing Service.