WEB Proxy dropped my customers

i have ran webproxy since this last monday and set available for cache 6gb from system drive, what i was not sure was for ram cache so i set unlimited, my router pc is a xeon 2.4ghz with 1024ddr and running on 10gb ide drive…

what i noticed was that every day the free memory was reducing until today it went down to 38megabytes of ram
(from 1gb ) and disk space was about 3 gb … suddenly system came down, customers could not surf and i was figuring out all day what happened…then decided to stop webproxy and cleared cache and everything started running again…
so my question is: was my error to setting it up with unlimited memory or is webproxy unstable and that is why it failed..

any comment would be appreciated.