Dell venue 11 Pro 7130 4300Y trouble with CPU usage maximum of 16%, can not higher.

Please help me, aome months recently my Dell run very slow, after tracked, i saw that there is trouble with my CPU usage as the image below:

Maximum usage of CPU just only 16-17% can not up, 

after restart more than 5 times, it increased maxumum to 54% but not more!. Maximum of 54-55%.

Please help me, my Dell run too slow, can not do anything !!! Thanks you so much.