What OS was the old dell, if it was XP and you had Service Pack 3 you need to use the UXTheme patcher or else when you install a custom theme it forgets up your computer really bad.
And if you use the UXTheme Patcher on a version of xp that is Service Pack 2 or 3 it just breaks nearly everything, you would need to go into safe mode an use the UX theme patching program to De-patch your computer.
Now if you where doing it on Vista or something the I don't have a clue, what I do know is that some themes from Deviant Art will forget up your PC sometimes.