error with installing theme

Hello
I’m somehow new with WordPress. I worked with my WP great and everything was going really good. I tried to install some plug-ins but i couldn’t…after that i can install anything at all specially my theme. i tried to upload my theme but it failed to install with showing this:

Unpacking the package…
Installing the theme…
Could not create directory. /var/www/vhosts/flyinghour.com/httpdocs/wp-content/themes/music-lovers/
Theme install failed.

i cant even install the themes i found through search button!!!
i would appreciate if anyone can help me to overcome this problem, and please just speak a bit nude as im new somehow