Which miner/OS are you using?
What hardware are you using?
Is your internet connection stable?
Which pools have you tried? Deepbit has been under DDoS attacks a couple of times the last few days as far as i know.
Windows + ufasoft - bitcoin-miner
Im using a 3 years old machine (it did not have any problems connecting to mining.bitcoin.cz, except when it was totally blocked by firewall)
Yes, internet connection is stable.
I tried deepBit, and mining.bitcoin.cz.
Any other(s) I should try ?
(Is there a list of all of them ?)