MacBookPro - can't empty trash -- operation cannot be completed.....

So for about a month or so my laptop will randomly go gray and say to shut down and restart.

For the past week or so randomly when I restart I will get a pop up window that says Start Up disk is getting full, compress files or delete files....(or something like that).

Well I ignored those -- always in a hurry -- and today I got the gray screen saying shut down and restart.

I restarted and got the top Finder bar and my screen saver but no files from my hard drive showed up on the screen -- and it would blink off and on -- blue and then the Finder bar with my screen saver.

I pushed all sorts of buttons and finally after many times of starting and restarting the hard drive files did come up.

I quickly tried to drag files into the trash -- but when I go to delete my trash I get a message "operation cannot be completed because you do not have sufficient privledges".

I simply cannot empty the trash.

When I research how to empty the trash some suggestions were to go to the disk utility -- I can click on that but nothing at all starts up.

I've also held down the trash icon and used the option key and then let go of it -- nothing empties -- just the same message over and over again --

I need suggestions on how to get this stuff off my desktop/hard drive so that I have more room -- but it seems that no matter what I do the trash is frozen and I can't get anything to work on the start up disk.

help please!