Well...I think I'd update IE and Outlook to IE8 and Outlook whatever...your current install may be damaged and in need of replacement/reinstall.
But...the file opening thing...that seems like more of a Windows problem. I would test some files which are not in OE/emails to confirm that XP is working properly.
<<It's not a virus or anything because my computer was just reformated like 2-3 weeks ago and I haven't opened any strange e-mails.>>
I don't want to ruin your good thoughts...but 2-3 weeks ago is an awfully long time...when you think about the fact that you can go to any number of websites and become unknowingly infected within seconds. And...a reformat is not equivalent to installing a reliable AV program, supplemented by a couple of malware-defense programs.
If you Google/read up on any of the zillion fake AV malware items that exist today...you'll find that it doesn't take much effort to become infected these days. There are many more sophisticated methods used than email.
Edited by hamluis, 26 September 2010 - 05:11 PM.