cpu stuck at 1.20ghz

my cpu, core i3-540 is always stuck at 1.20ghz, even though the base speed is 3.06ghz. the imac is running windows 10 with no partition for macos. this started after i replaced the gpu with a hd-6750.

crwdns2934089:0crwdne2934089:0 crwdns2934093:0crwdne2934093:0

crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 0
crwdns2934285:0crwdne2934285:0