Quote: Originally Posted by mobius101
....start with 70-80 and it drops after few seconds to 30
That could be normal - it depends on the volume of files, and file sizes. The faster speed is often referred to as the burst speed, which drops off to a smaller number which is referred to as the sustained speed, but usually this is only noticeable with large files.
Wolfgang mentioned defragmentation - in addition, you might also want to perform a chkdsk /R
on the disk/s if there are bad sectors.