I have a destop PC running Win XP Pro SP2 (GigaByte GA 7VT600 motherboard, Sempron 2800+ CPU, 512 MB DDR, ATI RADEON 9200, Maxtor 120 GB ATAPI HD) and all of a sudden PC started performing poorly (jerky video, slow booting, etc.). I benchmarked the system with Dr. Hardware 6.0 and it showed big decrease in hard disk performance - 1/10 of previously measured read/write/access times (RAM, CPU and video staying the same as in earlier tests). CHKDSK check did reveal nothing (no bad sectors, no problems). I ran defragmentation utility and it worked fine. System is protected with WinXP SP2 Firewal and is constantly auto updated. Norton AntiVirus is also doing its job (latest definitions). System is used as a home PC (games, MS Office apps, moderate internet use). HD's file system is NTFS.
What could be wrong ?