copying & decrypting files

I would greatly appreciate it if anyone can help me with this.

Because of virus infestation I decided to format my hard drive, but before doing so I copied my important encrypted files into an external hard disk. After the format I re-installed the same OS that was originally pre-installed in my computer by the manufacturer: Windows XP Media Center Ver. 2005, SP 2. I used the same User Names and passwords as before, but when I tried to copy my encrypted files back from my external drive to my main hard drive I get the error message "Access Denied". I also tried decypting the files in the external drive but I always get the same "Access Denied" message. I spent hours reading about the EFS but it was too complicated and too technical for me.

Any ideas, anyone? I thank you in advance

orestrada