catalog price rules- most killing part in magento, it may be because of many reasons -
cron jobs in server not working & wrong configuration in backend , difference in
magento time , check this link once .
regarding installing extension, please tell how you tried to install [ through magento connect ? ] if so , Alternatively you can install the extension through FTP (like FileZilla).
It's not safe to use Magento connect for installing extension , click this link for more information.
in the worst case, if you want immediate solution , Alternatively you can install the extension through FTP (like FileZilla). You can paste the extension key in this unofficial link and you can download the extension files. Let me know if you find any problems in this.
Note : As this is unofficial 3rd party site, there is no guarantee about security. but i tested many extensions, i did't faced any security problems....