title says it all:
Geth syncing stucks at block 2721823 ... I downloaded the newest version 1.5.4, started first with the flag
-removedb, than with
-fast -cache 2048.
Everything went smooth, untill this block.
Each time the Wallet is started it needs to sync the chain with the network. The first time it needs to download and verify the entire chain which can take a long time. Therefore a smarter and faster solution is used the first time the Wallet is started. It will not download and verify the entire chain but will only download specific parts up to a specific block (latest block - 1024 blocks). After that it will download and process the state of the contracts which can take quite some time. So please wait an let it finish downloading the state, otherwise it would start from scratch again. You can find more details here.