Yep! You fell into the trap! A '''''Fixed''''' SATA III (6.0 Gb/s) SSD won’t play well in a SATA II (3.0 Gb/s) system! You need either a '''''Fixed''''' SATA II (3.0 Gb/s) or a '''''Auto Sense''''' SATA III drive to work properly in your system.
OK what is this '''''Fixed''''' and '''''Auto Sense''''' all about? Basically, When SATA III was introduced the drive makers got a lot of returned drives which popped claimed didn’t work in their systems (which was true!) At that point a few drive makers created a new series of drives which senses the systems SATA port’s I/O data rate and match it! Its similar to how your systems Ethernet speed is deduced from 10, 100 MBPS or even 1GBPS. But just like Ethernet plugging in an older fixed speed 100GB connection into a 10MBPS hub won’t work!
So lets find one of these Auto Sense drives like [https://s3.ap-northeast-2.amazonaws.com/global.semi.static/Samsung_SSD_870_EVO_Data_Sheet_Rev1.1.pdf|Samsung 870 EVO] if we look at this spec sheet we find the '''Interface''' line shows us: '''”SATA 6 Gb/s Interface, compatible with SATA 3 Gb/s & 1.5 interfaces”''' So this drive is able to match to your systems slower SATA port! Now lets look at the [https://www.adata.com/upload/downloadfile/Datasheet%20-%20Ultimate%20SU650_EN_201809.pdf|ADATA SU650] we see the Interface line only lists '''SATA 6Gb/s (SATA III)''' which is a Fixed speed drive!
So stop pulling out your hair! Find either a Fixed speed SATA II (3.0 Gb/s) drive or a drive which clearly states SATA II (3.0 Gb/s) support like the Auto Sense Samsung SSD.