You could get a new switch (should be able to pick one up at most hardware stores, just make sure you get the kind that only make contact when pushed in). Then plug this in along with the old switch (to keep all the rest of the functionality of that ribon cable like front audio). You could either do some case modding to fit the new switch in or just have it sit outside the case.
That may be the easiest option. Of course, I found out where I worked this summer how to easily take Dell cases apart... Let the shelf they are sitting on collapse as 30 systems (which I'd like to go on record as saying I thought it was stacked a little too much!) fall to the ground. All kidding aside, the Dell cases are actually really tough and believe it or not, most of those systems survived the approx. 6 foot fall (except for 2, which I rebuilt into 1 from the good parts from eacy). I found though, that if you keep working with a Dell case, and slowly try to take it apart, making note of where they have all their clips and such so you know which way to pull, you can eventually get them apart, in which case you could replace or try to fix the current switch.
That may be the easiest option. Of course, I found out where I worked this summer how to easily take Dell cases apart... Let the shelf they are sitting on collapse as 30 systems (which I'd like to go on record as saying I thought it was stacked a little too much!) fall to the ground. All kidding aside, the Dell cases are actually really tough and believe it or not, most of those systems survived the approx. 6 foot fall (except for 2, which I rebuilt into 1 from the good parts from eacy). I found though, that if you keep working with a Dell case, and slowly try to take it apart, making note of where they have all their clips and such so you know which way to pull, you can eventually get them apart, in which case you could replace or try to fix the current switch.