where have you got dosbox from?
what are your PC specifications?

post content of "DOSBox Status Window" (in Windows: right click on its title bar -> edit)
enclose your dosbox's config file

Dosbox downloaded from the "Windows" link here: http://www.dosbox.com/download.php?main=1

System spec:
Windows Vista Home Premium 64
AMD Phenom II x4 945 3ghz
8gb RAM
nVidia Geforce 9600GT 1gb RAM

Dosbox Status Window:
DOSBox version 0.74
Copyright 2002-2010 DOSBox Team, published under GNU GPL.
---
CONFIG:Loading primary settings from config file C:\Users\Dave\AppData\Local\DOSBox\dosbox-0.74.conf
Memory sizes above 31 MB are NOT recommended.
Stick with the default values unless you are absolutely certain.
MIDI:Opened device:win32

Config file is attached.

If you need any more info, let me know. Thanks for the help.

do other dosbox's shortcuts work? check them all and tell results

Nope, none of the CTRL+"button" combinations seem to work. I initially thought that the keys had been remapped some how, so I tried CTRL+F1 to change them, nothing happened. I've also used the Reset KeyMapper.bat in case something had gone wrong, still the same result as before though.

check manual for windib

Just tried that, still no luck. My Shift+"button" all work, just the CTRL+"button" that aren't. Also checked the thread shown in the manual, I don't have an extra devices. I've just got a standard PS/2 keyboard under (Keyboard) and a USB wheel mouse (under Human Interface Devices).

does ctrl work in windows? try ctrl-alt-del

Yep, it works fine in Windows.

Just tested something that seems odd, which may be of help. In Dosbox if I use CTRL+(any letter) it brings up strangle symbols (smiley faces, "playing card suits" - heart, club, diamond, spade etc.), whereas in a command prompt it shows an "up" arrow plus the letter pressed.

I don't think it's the CTRL button that's the problem. I was playing Wing Commander 4 earlier and none of the "F" buttons worked.

you said alt-f shortcuts worked, so once again:

robertmo wrote:

do other dosbox's shortcuts work? check them all and tell results

Alt-Pause and Alt-Enter both work as they should. Alt-F12 nothing happens.

do f keys work in windows?

I am officially an idiot. The F keys weren't working in Windows either. A quick look at the Microsoft website mentioned a F Lock key on the keyboard (I didn't even know such a thing existed)... once I pressed it they all work, including in Dosbox.

Sorry for wasting your time, but thanks for all the help.

Just as a rough guide:
3000 cycles: 386SX-20
6000 cycles: 386DX-33
12000 cycles: 486DX-33
24000 cycles: 486DX2-66