Usual reason is the use of smaller or older graphics cards which are not able, powerwise, to punch in with the tex's.
Solution!

Go to d/l section of this site - into Search - Type in Tony Gould - hit enter..... and you will get a list of default a/c Tex' enhancers which will give you bright happy tex's for yr defaults.
If card and sys are reasonably high move tex slider bottom right of display settings page over to high or max.
However by look of blurries suggest1 is yr answer.