How to solve network problems with Windows Server 2008 R2?

Question

Computer networks

Good afternoon! On Windows Server 2008, the connection has been dropping for literally a few seconds recently, it simply becomes unavailable. DHCP, DNS, domain, file sharing and terminal 1s are spinning on it (accounting via RDP enters the server and works on it in 1s). The network is small, there are 25 computers, 6 people (accounting) work with 1s, and somewhere by lunchtime they begin to complain about the slowdown of 1s and the entire network as a whole.
Server:
Processor: Intel Xeon CPU X322 2.4 GHz (4 cores)
RAM: 8 Gb
Network (not built-in): Intel Gigabit CT2 Desktor Adapter
Hardware Raid 1 (1 Tb)
The server, like all computers, is connected to Allied Telesis AT-FS750/ 24 (24 lan + 2 SFP + VGA)
Network advanced settings:
Gigabit Master Slave Mode - Auto Detect
Interrupt Moderation - Enabled
Jumbo Packet - Disabled
Large Send Offload v2 (IPv4) - Enabled
Large Send Offload v2 (IPv6) - Disabled
Locally Administered Address - empty
Log Link State Event - Enabled
Performance Option - I poke in Properties and get:
Adaptive Inter-Frame Spacing - Disabled
Flow Control - Rx & Tx Enabled
Interrupt Moderation Rate - Adaptive
Receive Buffers - 256
Transmit Buffers - 512
Priority & VLAN - Priority & VLAN Enabled
TCP / IP Offloading Options - again, Properties and checkboxes are on each item:
IPv4 Checksum Offload
TCP Checksum Offload (IPv4)
TCP Checksum Offload (IPv6)
UDP Checksum Offload (IPv4)
UDP Checksum Offload (IPv6)
Wait for Link - Auto Detect Offsite
drivers are the latest. If you need any more information, I will write.
Thanks in advance)
PS I myself am not a system administrator (the company cannot afford it, but I have to do it)

Answer 1

Pings go, rdp does not break, but the computer is not available