Have your XP CD handy and click Start, Run, and type in
sfc /scannow (with a space between the c and the /)
System File Checker will look at your system and using the XP CD replace the missing files.
I tried speeding up my computer last week by removing useless files, and I ended up taking out needed files. But when I start my computer, it shows "cannot find (series of little squares)" Then another screen tells me to remove the file names - series of little squares. How can I fix this problem?