Re-Carbonating beer in Keg

Hi all,
I brewed an ESB and a porter in time Christmas 2012. I kegged both batches and both beers turned out great. Over the next 2 months I drank 1/2 of each. Then due to some medication I was taking for several months I was advised not to drink alcohol. Unfortunately my 5lb CO2 ran out of CO2 and I did not realize it until I tapped a beer last weekend, and found that both beers were flat. No carbonation.

If I recarbonate my beer will it affect the quality of my beer? Or should I just dump the beer and put it down to experience?

Thanks

If the beers are still clean, I would definitely re-carbonate and enjoy them...

Cheers!

[edit] The porter may even have improved. The ESB probably not so much.

Thanks I will give it a try

So how did you go about that? By adding new sugar and yeast? And how did it turn out? Having a bit of a flat pale ale issue myself....