I've had coins in the wallet for 1809 conformations and had the wallet open and unlocked for days and not seen the coins mature or gotten any stakes. I've tried on multiple machines (both win7) and tried opening and closing the wallet and redownloading the blockchain multiple times to no effect. If it helps calling getstakinginfo from the console gives
{
"enabled" : true,
"staking" : false,
"errors" : "",
"currentblocksize" : 3392,
"currentblocktx" : 7,
"pooledtx" : 7,
"difficulty" : 0.00000095,
"search-interval" : 1,
"weight" : 0,
"netstakeweight" : 4,
"expectedtime" : -1
}
I'm on Win 7 as well and it's working fine.
Is your wallet 24,373,760 bytes?