Iam using yahoo messenger10.0 but when i sign in

The error message would be useful - if you have problems signing in
Try each of these in turn and give feedback please for others.
1) Start with a clean browser
Download 'ccleaner' and run it through a couple of times,using the factory settings and the 'Run Cleaner' control until 0 bytes are seen to be cleaned following a scan
Run the 'Registry' from the left hand toolbar but 'Save' any changes after opting to 'repair' errors.
http://www.filehippo.com/download_ccleaner/
2) On the sign in page click 'Messenger' > Conection
Toggle between 'Connect direct to the internet' and 'Proxy setting' make sure the information is correct in the lower 2 boxes
3) Check these settings in IE (even if you have another browser set as default)
a) Tools > Internet options > Connections > Lan settings > check 'Automatically detect settings - uncheck other options
b) Tools > work offline - make sure this is NOT checked and has a red X through it
4) Disable your firewall and do a trial sign in
5) Control Panel > Internet Options > Connections > Lan Settings-uncheck Proxy server and check automatically detect setting
Control Panel > Internet Options > Connections > dial-up and virtual private Network setting > select your default connection > setting > check automatically detect setting

I advice you to reinstal the program maybe you did something wrong during instalation.