Here is my answer and this may help. If you tried a new cam, and it still boots to logo then shuts off then does it over and over.. try another screen. Some screens are cheaply made and won’t register with the boot up process and will fail causing the boot loop. Try putting the old screen on and seeing if it’ll boot. If it does, your screen is bad and should be replaced with a higher quality display. I had one come in from a shop same issue and it ended up being a cheap quality replacement screen causing the boot loop.
No it's not, Unsure why you are telling him false information. The hard drive is soldered EMMC flash based hard drive and is not upgradeable... However though, there is a guide using your existing WIFI Lan Port to get a bigger SSD inside this laptop and upgrade available here: HP Stream 13 Disassembly for Upgrading the PCIe mini SSD
If it dies fast and you tested the battery, you have a faulty U2 IC chip and needs to be replaced and resoldered! A board level technician will be able to replace it for you! Also using third party cables and modified cables can also blow the U2 IC Tristar chip on the board and you get those symptoms!
Run the extended version of the Apple Hardware Test. Sometimes you will get an error if you run the quick version, and it may be something of a false positive. Some have found doing an SMC reset 3 or 4X can eliminate the error (note: a work around not a fix). If it is indeed a logic board error it points to a sensor(s) failing, VPOR might be VGC(VPU) related. You'll probably need a new logic board, AFAIK sensors as well as the VGC are soldered to the logic board which pretty much makes them non-DIY repairs, as soldering on logic boards are not for amateurs.