Newb i3 pro b issues

Hi. Firstly thanks for this great informational forum.

Ok i have purchased a geeetech i3 pro b 3d printer and after setting up have a couple of questions/ issues.

1. The headbed temp seems to be not what it is. I put some tape on it so i can point my ir heat gun at it and the bed was set at 120 for abs but its only getting to 45-60 but then says its at temp of 120c.
The thermister seems to be ok at normal temp as when the machine is off both the extruder temp and bed temp show the same.

2. When it initializes the bed comes forward to max then its like it tries to go further but cant and the motor just makes a loud noise for 20seconds ish. When i print it does go into the centre and its ok but its like it doesnt know where the end is y_.

3. When printing the first few layers about 4mm thick seem to be ok but then its like the whole thing comes off the bed and it just drags it around. (Im thinking this could be something to do with the headbed temp.

4. I notice the z thread rods are poor quality and keep jamming and closer inspection i can see they have tiny shards of metal in the groves. I did read a better upgrade is ballscrew but how would i change over because im thinking the firmware is designed for threadrod.

I think thats all for now.

Thanks and look forward to some helping answers


stu