Can the singer one plus computerized sewing machine be opened up to fix something on inside?

Use https://www.google.com with the search terms singer 7258 parts
Example of search results:

https://www.sewingpartsonline.com/singer-7258-stylist-parts.aspx?sort.ss_cat_sort=desc&index=9

have you tried contacting singer about the problem, it could be a sensor, if it's malfunctioning, having it replaced may be the only way to fix the problem,, if it's still under warrenty, they may have you take it to a sewing machine shop to repair it..
here are 2 links to see if singer can help you with the problem
Contact Us Singer Sewing

Products Singer Sewing Co

take it in far a warranty service check
the needle breaking may have altered something or broke something inside

Find a Singer dealer and see if they can help. This is NOT something you should try to fix yourself. I wouldn't let them send it out. The repair shop needs to be at the dealer. Your machine is too expensive for DIY and any attempts will void your ability to have Singer fix it.

Contact your Brother dealer and ask if this is something you can fix.

If this mechanism is inside the machine, you may do more harm and that could result in more expense and invalidate your warranty.

If the loops are on the bottom it means either the top tension is too loose or the lower tension is too tight. It can also mean that the thread is snagging on something in the bobbin case area.
sewman7

No, my problem is still not fixed, but being unemployed I can't afford to purchase a plan, I thought this information was free sorry. Thank you

http://www.singerco.com/accessories/manuals.htmlSinger

There is a manual and some helps here.