and what is your other pc?
make everything the same as on that one

it's an older laptop with 2 ghz 512 mb ram and XP.
i made everything the same
Could it be that my pc is to good?

do this with both systems:

post content of "DOSBox Status Window" (in Windows: right click on its title bar -> edit)
enclose your dosbox's config file (also include your MOUNT lines under [autoexec] section)

config:[autoexec]
# Zeilen in diesem Abschnitt werden beim Start von DOSBox als Befehle ausgeführt:
mount c "c:\games\"
mount D "F:\" -t cdrom
c:
cd heroes
heroes

dosbox status window:
DOSBox version 0.73
Copyright 2002-2009 DOSBox Team, published under GNU GPL.
---
CONFIG:Loading primary settings from config file dosbox.conf
MIDI:Opened device:win32
DOS keyboard layout loaded with main language code GR for layout gr

reinstall dosbox to c:\dosbox

doesn't work

where have you got dosbox from?
post content of "DOSBox Status Window"

The host hardware should have no influence on the emulated game, other than the speed of the emulation. That's what emulators are for after all (; .

Here's some ideas:

mount D "F:\" -t cdrom

Is the host CD drive letter the same on both machines? You could try creating an image of the CD (much more convenient anyway) and mounting it with the "imgmount" command.

Have you double-checked the mountings and made sure all files are available to DOSBox when the emulation starts? To do this "rem" the lines that will auto-start the game, start DOSBox and issue "dir" commands for c: and d: .

If you've copied the already installed files from the "old" machine to the "new" one: are you sure that the game data on both machines is identical? This can be checked with a "file comparing" tool, Total Commander i.e. has the functionality built in. You should byte-compare each file to make sure everything is there.

Are you using the exact same DOSBox version on both machines?

You could also try different "output" values in dosbox.conf to see if the new system has problems with certain outputs. That's probably not the case though.