What errors are displayed when you try to open them ?
Can you give some examples of the file names, malware name and location of the file/s.
Check the avast! Log Viewer (right click the avast 'a' icon), Warning section, this contains information on all avast detections. Or check the source file using notepad C:\Program Files\Alwil Software\Avast4\DATA\log\Warning.log
You may have to try using some other file management software if you are unable to use explorer or connect the drive as a slave on another system to try and access that log file. See,
http://www.snapfiles.com/Freeware/system/fwfilemanagement.html.
It looks like you have a serious infection for it to have infected 324 files and your system could be too compromised to be recovered.
Deletion isn't really a good first option (you have none left), 'first do no harm' don't delete, send virus to the chest and investigate.