What Debian is it? How updated?
Use Synaptic to see what broken packages you might have. We'll take it from there then.
Here's how I installed "screen";
root@Alan-Laptop:/var/lib/dpkg/info# apt-get install screen
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following NEW packages will be installed:
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 605 kB of archives.
After this operation, 1,008 kB of additional disk space will be used.
Get:1 http://ftp.hr.debian.org/debian/ squeeze/main screen i386 4.0.3-14 [605 kB]
Fetched 605 kB in 1s (435 kB/s)
Reading package fields... Done
Reading package status... Done
Retrieving bug reports... Done
Parsing Found/Fixed information... Done
Selecting previously deselected package screen.
(Reading database ... 187013 files and directories currently installed.)
Unpacking screen (from .../screen_4.0.3-14_i386.deb) ...
Processing triggers for man-db ...
Processing triggers for install-info ...
Setting up screen (4.0.3-14) ...