Help! My PCIE Slots Aren’t Working on My New Motherboard

Hey everyone, I need some help! I just got a new prebuilt tower with a TUF GAMING Z890 Plus WiFi motherboard. Everything was going great until I tried to install my new graphics card, an NVIDIA GeForce RTX 5070 Ti. At first, I couldn't get it to work—no image and the fans weren't even moving. After some investigation, I discovered that a metal support for the preinstalled graphics card was blocking the top PCIE slot. I removed that support, got the card properly seated, and it lit up with spinning fans, which was awesome! But then, I hit another snag: I'm still not getting any image. Checking the BIOS, it shows that the PCIE slot is "Device: Not detected." Even the other slots (for the WiFi and sound card) are showing as "Not detected.") This wasn't the case before I started messing around with the BIOS. I think I might have accidentally messed something up there. I tried changing the PCIE settings manually, but nothing seems to be working. During boot, the motherboard shows a sequence of colored LEDs before turning off, which gives me some hope that everything is fine. My build includes an Intel Core Ultra9 285K, 64 GB of DDR5-6000 RAM, and a 12V power supply that's more than capable for this setup. Has anyone encountered this issue or have any advice? I'm hesitant to send the whole PC back since that could take a while and I'd prefer to troubleshoot it first!